Diesel Particulate Matter Exposure of Underground Metal and Nonmetal
Miners [01/19/2001]
Volume 66, Number 13, Page 5706-5755
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DEPARTMENT OF LABOR
Mine Safety and Health Administration
30 CFR Part 57
RIN 1219-AB11
Diesel Particulate Matter Exposure of Underground Metal and
Nonmetal Miners
AGENCY: Mine Safety and Health Administration (MSHA), Labor.
ACTION: Final rule.
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SUMMARY: This rule establishes new health standards for underground
metal and nonmetal mines that use equipment powered by diesel engines.
This rule is designed to reduce the risks to underground metal and
nonmetal miners of serious health hazards that are associated with
exposure to high concentrations of diesel particulate matter (dpm). DPM
is a very small particle in diesel exhaust. Underground miners are
exposed to far higher concentrations of this fine particulate than any
other group of workers. The best available evidence indicates that such
high exposures put these miners at excess risk of a variety of adverse
health effects, including lung cancer.
The final rule for underground metal and nonmetal mines would
establish a concentration limit for dpm, and require mine operators to
use engineering and work practice controls to reduce dpm to that limit.
Underground metal and nonmetal mine operators would also be required to
implement certain ``best practice'' work controls similar to those
already required of underground coal mine operators under MSHA's 1996
diesel equipment rule. These operators would also be required to train
miners about the hazards of dpm exposure.
By separate notice, MSHA has published a rule to reduce dpm
exposures in underground coal mines.
DATES: The provisions of the final rule are effective March 20, 2001.
However, Sec. 57.5060 (a) will not apply until July 19, 2002 and
Sec. 57.5060 (b) will not apply until January 19, 2006.
FOR FURTHER INFORMATION CONTACT: David L. Meyer, Director, Office of
Standards, Regulations, and Variances, MSHA, 4015 Wilson Boulevard,
Arlington, VA 22203-1984. Mr. Meyer can be reached at dmeyer@msha.gov
(Internet E-mail), 703-235-1910 (voice), or 703-235-5551 (fax). You may
obtain copies of the final rule in alternative formats by calling this
number. The alternative formats available are either a large print
version of the final rule or the final rule in an electronic file on
computer disk. The final rule also is available on the Internet at
http://www.msha.gov/REGSINFO.HTM.
SUPPLEMENTARY INFORMATION:
I. Overview of the Final Rule
This Part: (1) Summarizes the key provisions of the final rule; and
(2) summarizes MSHA's responses to some of the fundamental questions
raised during the rulemaking proceeding--the need for the rule, the
ability of the agency to accurately measure diesel particulate matter
(dpm) in underground metal and nonmetal mine environments, and the
feasibility of the requirements for this sector of the mining industry.
(1) Summary of Key Provisions of the Final Rule
The final rule applies only to underground areas of underground
metal and nonmetal mines.
The final rule requires operators: (A) To observe a concentration
limit where miners normally work or travel by the application of
engineering controls, with certain limited exceptions, compliance with
which will be determined by MSHA sampling; (B) to observe a set of best
practices to minimize dpm generation; (C) to limit engines newly
introduced underground to those meeting basic emissions standards; (D)
to provide annual training to miners on dpm hazards and controls; and
(E) to conduct sampling as often as necessary to effectively evaluate
dpm concentrations at the mine. A list of effective dates for the
provisions of the rule follows this summary.
(A) Observe a limit on the concentration of dpm in all areas of an
underground metal or nonmetal mine where miners work or travel, with
certain specific exceptions. The rule would limit dpm concentrations to
which miners are exposed to about 200 micrograms per cubic meter of
air--expressed as 200DPM g/m 3. However,
the rule expresses the limit so as to reflect the measurement method
MSHA will be using for compliance purposes to determine dpm
concentrations. That method is specified in the rule itself. As
discussed in detail in response to Question 2, the method analyzes a
dust sample to determine the amount of total carbon present. Total
carbon comprises 80-85% of the dpm emitted by diesel engines.
Accordingly, using the lower boundary of 80%, a concentration limit of
200DPM g/m 3 can be achieved by
restricting total carbon to 160TC g/m 3.
This is the way the standard is expressed:
After January 19, 2006 any mine operator covered by this part
shall limit the concentration of diesel particulate matter to which
miners are exposed in underground areas of a mine by restricting the
average eight-hour equivalent full shift airborne concentration of
total carbon, where miners normally work or travel, to 160
micrograms per cubic meter of air (160TC g/m
3).
All underground metal and nonmetal mines would be given a full five
years to meet this limit, which is referred to in this preamble as the
``final'' concentration limit. However, starting July 19, 2002,
underground metal and nonmetal mines have to observe an ``interim'' dpm
concentration limit--expressed as a restriction on the
[[Page 5707]]
concentration of total carbon of 400 micrograms per cubic meter
(400TC g/m 3). The interim limit would
bring the concentration of whole dpm in underground metal and nonmetal
mines to which miners are exposed down to about 500 micrograms per
cubic meter. No limit at all on the concentration of dpm is applicable
for the first eighteen months following promulgation. Instead, this
period would be used to provide compliance assistance to the metal and
nonmetal mining community to ensure it understands how to measure and
control diesel particulate matter concentrations in individual
operations.
In general, a mine operator has to use engineering or work practice
controls to keep dpm concentrations below the applicable limit. The use
of administrative controls (e.g., the rotation of miners) is explicitly
barred. The use of personal protective equipment (e.g., respirators) is
also explicitly barred except in two situations noted below. An
operator can filter the emissions from diesel-powered equipment,
install cleaner-burning engines, increase ventilation, improve fleet
management, or use a variety of other readily available controls; the
selection of controls is left to the operator's discretion.
Special extension. The rule provides that if an operator of a metal
or nonmetal mine can demonstrate that there is no combination of
controls that can, due to technological constraints, be implemented by
January 19, 2006, MSHA may approve an application for an additional
extension of time to comply with the dpm concentration limit. Such a
special extension is available only once, and is limited to 2 years. To
obtain a special extension, an operator must provide information in the
application adequate for MSHA to ensure that the operator will: (a)
Maintain concentrations at the lowest limit which is technologically
achievable; and (b) take appropriate actions to minimize miner exposure
(e.g., provide suitable respiratory protection during the extension
period).
It is MSHA's intent that primary responsibility for analysis of the
operator's application for a special extension will rest with MSHA's
district managers. District managers are the most familiar with the
conditions of mines in their districts, and have the best opportunity
to consult with miners as well. At the same time, MSHA recognizes that
district managers may need assistance with respect to the latest
technologies and solutions being used in similar mines elsewhere in the
country. Accordingly, the Agency intends to establish within its
Technical Support directorate in Arlington, Va., a special panel to
consult on these issues, to provide assistance to district managers,
and to give final approval of any application for a special extension.
Special rule for employees engaged in inspection, maintenance or
repair activities. The final rule provides that with the advance
approval of the Secretary, employees engaged in such activities may
work in concentrations of dpm exceeding the applicable concentration
limit. However, the Secretary may only approve such work under three
circumstances: when the activities are to be conducted are in areas
where miners work or travel infrequently or for brief periods of time;
when the miners work exclusively inside enclosed and environmentally
controlled cabs, booths and similar structures with filtered breathing
air; or when the miners work in shafts, inclines, slopes, adits,
tunnels and similar workings that are designated as return or exhaust
air courses and that are used for access into the mine or egress from
the mine. Moreover, to approve such an exception, the Secretary must
determine that it is not feasible to reduce the concentration of dpm in
these areas, and that adequate safeguards (including personal
protective equipment) will be employed to minimize the dpm exposure of
the miners involved.
An operator plan providing such details must be submitted; it is
MSHA's intent to review these in the same manner as applications for a
special extension. Such plans can only be approved for one year, but
may be resubmitted each year.
Compliance determinations with concentration limit. Measurements to
determine noncompliance with the dpm concentration limit will be made
directly by MSHA, rather than having the Agency rely upon operator
samples. Under the rule, a single Agency sample, using the sampling and
analytical method prescribed by the rule, is explicitly deemed adequate
to establish a violation.
The rule requires that if an underground metal or nonmetal mine
exceeds the applicable limit on the concentration of dpm, a diesel
particulate matter control plan must be established and remain in
effect for 3 years. The purpose of such plans is to ensure that the
mine has instituted practices that will demonstrably control dpm levels
thereafter. Reflecting current practices in this sector, the plan does
not have to be preapproved by MSHA. The plan must include information
about the diesel-powered equipment in the mine and applicable controls.
The rule requires operator sampling to verify that the plan is
effective in bringing dpm levels down below the applicable limit, using
the same sampling and analytical methods as MSHA, with the records kept
at the mine site with the plan to facilitate review. Failure of an
operator to comply with the requirements of the dpm control plan or to
conduct adequate verification sampling is a violation of the rule; MSHA
is not be required to sample to establish such a violation.
(B) Observe best practices. The rule requires that operators
observe the following best practices to minimize the dpm generated by
diesel-powered equipment in underground areas:
Only low-sulfur (0.05% or less) diesel fuel may be used.
The rule does not at this time require the use of ultra-low sulfur fuel
by the mining community. MSHA is aware that the Environmental
Protection Agency issued final regulations addressing emissions
standards (December 2000) for new model year 2007 heavy-duty diesel
engines and the low-sulfur fuel rule. The regulations require ultra-low
sulfur fuel be phased in during 2006-2010.
Only EPA-approved fuel additives may be used.
Approved diesel engines have to be maintained in approved
condition; the emission related components of non-approved engines have
to be maintained in accordance with manufacturer specifications; and
any installed emission devices have to be maintained in effective
operating condition.
Equipment operators are authorized and required to tag
equipment with potential emissions-related problems, and tagged
equipment has to be promptly referred for a maintenance check by
persons qualified by virtue of training or experience to perform the
maintenance.
(C) Limit newly introduced engines to those meeting basic emission
standards. The rule requires that, with the exception of diesel engines
used in ambulances and fire-fighting equipment, any diesel engines
added to the fleet of an underground metal or nonmetal mine after
January 19, 2001 must either be an engine approved by MSHA under Part 7
or Part 36, or an engine meeting certain EPA requirements on
particulate matter specified in the rule. Since not all engines are
MSHA approved, this ensures a wide variety of choice in meeting the
engine requirements of this rule.
(D) Provide annual training to miners on dpm hazards and controls.
Mines using diesel-powered equipment must annually train miners exposed
to dpm
[[Page 5708]]
in the hazards associated with that exposure, and in the controls being
used by the operator to limit dpm concentrations. An operator may
propose including this training in the Part 48 training plan.
(E) Conduct sampling as often as necessary to effectively evaluate
dpm concentrations at the mine. The purpose of this requirement is to
assure that operators are familiar with current dpm concentrations so
as to be able to protect miners. Since mine conditions vary, MSHA is
not requiring a specific schedule for operator sampling, nor a specific
sampling method. The Agency will evaluate compliance with this sampling
obligation by reviewing evidence of operator compliance with the
concentration limit, as well as information retained by operators about
their sampling. Consistent with the statute, the rule requires that
miners and their representatives have the right to observe any operator
monitoring--including any sampling required to verify the effectiveness
of a dpm control plan.
Summary of Effective Dates. As of March 20, 2001, operators must
comply with the requirement that new engines added to a mine's
inventory be either MSHA approved or meet the listed EPA standards.
As of March 20, 2001, underground metal and nonmetal mine operators
must comply with the requirement to provide basic hazard training to
miners who are exposed underground to dpm and the best practice
requirements listed above under (B).
As of July 19, 2002, underground metal and nonmetal mine operators
must also comply with the interim dpm concentration limit of 400
micrograms of total carbon per cubic meter of air.
Finally, as of January 19, 2006, all underground metal and nonmetal
mines have to comply with a final dpm concentration limit.
MSHA intends to provide considerable technical assistance and
guidance to the mining community before the various requirements go
into effect, and be sure MSHA personnel are fully trained in the
requirements of the rule. A number of actions have already been taken
toward this end. The Agency held workshops on this topic in 1995 which
provided the mining community an opportunity to share advice on how to
control dpm concentrations. The Agency has published a ``toolbox'' of
methods available to mining operators to achieve reductions in dpm
concentration, often referred to during the rulemaking proceedings.
MSHA also developed a computer spreadsheet template which allows an
operator to model the application of alternative engineering controls
to reduce dpm, which it has published in the literature and
disseminated to the mining community. The Agency is committed to
issuing a compliance guide for mine operators providing additional
advice on implementing the rule.
A note on surface mines. Surface areas of underground mines, and
surface mines, are not covered by this rule. In certain situations the
concentrations of dpm at surface mines may be a cause for concern:
e.g., production areas where miners work in the open air in close
proximity to loader-haulers and trucks powered by older, out-of-tune
diesel engines, shops, or other confined spaces where diesel engines
are running. The Agency believes, however, that these problems are
currently limited and readily controlled through education and
technical assistance. The Agency would like to emphasize, however, that
surface miners are entitled to the same level of protection as other
miners; and the Agency's risk assessment indicates that even short-term
exposures to concentrations of dpm like those observed may result in
serious health problems. Accordingly, in addition to providing
education and technical assistance to surface mines, the Agency will
also continue to evaluate the hazards of diesel particulate exposure at
surface mines and will take any necessary action, including regulatory
action if warranted, to help the mining community minimize any hazards.
(2) Summary of MSHA's Responses to Several Fundamental Questions About
This Rule
During the rulemaking proceeding, the mining community raised some
fundamental questions about: (A) The need for the rule; (B) the ability
of the agency to accurately measure diesel particulate matter (dpm) in
underground metal and nonmetal mine environments; and (C) the
feasibility of the requirements for this sector of the mining industry.
MSHA gave serious considerations to these questions, has made some
adjustments in the final rule and its economic assessment as a result
thereof, and has provided detailed responses in this preamble. These
responses are briefly summarized here.
(A) The need for the rule. MSHA has to act in accordance with the
requirements of the Mine Safety and Health Act. Section 101(a)(6)(A) of
the Act specifies that any health standard must:
* * * [A]dequately assure, on the basis of the best available
evidence, that no miner will suffer material impairment of health or
functional capacity even if such miner has regular exposure to the
hazards dealt with by such standard for the period of his working
life.
The Mine Act also specifies that the Secretary of Labor
(Secretary), in promulgating mandatory standards pertaining to toxic
materials or harmful physical agents, base such standards upon:
* * * [R]esearch, demonstrations, experiments, and such other
information as may be appropriate. In addition to the attainment of
the highest degree of health and safety protection for the miner,
other considerations shall be the latest available scientific data
in the field, the feasibility of the standards, and experience
gained under this and other health and safety laws. Whenever
practicable, the mandatory health or safety standard promulgated
shall be expressed in terms of objective criteria and of the
performance desired. [Section 101(a)(6)(A)].
Thus, the Mine Act requires that the Secretary, in promulgating a
standard, based on the best available evidence, attain the highest
degree of health and safety protection for the miner with feasibility a
consideration. (More information about what constitutes ``feasibility''
is discussed below in item C).
In proposing this rule, MSHA sought comment on its risk assessment,
which it published in full as part of the preamble to the proposed
rule. In that risk assessment, the agency carefully laid out the
evidence available to it, including shortcomings inherent in that
evidence. Although not required to do so by law, MSHA had this risk
assessment independently peer reviewed, and incorporated the reviewers
recommendations. The reviewers stated that:
* * * principles for identifying evidence and characterizing
risk are thoughtfully set out. The scope of the document is
carefully described, addressing potential concerns about the scope
of coverage. Reference citations are adequate and up to date. The
document is written in a balanced fashion, addressing uncertainties
and asking for additional information and comments as appropriate.
(Samet and Burke, Nov. 1997).
Based on the information in that risk assessment, the agency made
some tentative conclusions. First, its tentative conclusion that miners
are exposed to far higher concentrations of dpm than anybody else. The
agency noted that median concentrations of dpm had been observed in
individual dieselized metal and nonmetal underground mines up to 180
times as high as average environmental exposures in the most heavily
polluted urban areas and up to 8 times as high as median exposures
estimated for the most heavily exposed
[[Page 5709]]
workers in other occupational groups. Moreover, MSHA noted its
tentative conclusion that exposure to high concentrations of dpm can
result in a variety of serious health effects. These health effects
include: (i) Sensory irritations and respiratory symptoms serious
enough to distract or disable miners; (ii) premature death from
cardiovascular, cardiopulmonary, or respiratory causes; and (iii) lung
cancer. After a review of all the evidence, MSHA tentatively concluded
that:
(1) The best available evidence is that the health effects
associated with exposure to dpm can materially impair miner health or
functional capacity.
(2) At levels of exposure currently observed in underground mining,
many miners are presently at significant risk of incurring these
material impairments over a working lifetime.
(3) The reduction in dpm exposures that is expected to result from
implementation of the rule proposed by the agency for underground metal
and nonmetal mines would substantially reduce the significant risks
currently faced by underground metal and nonmetal miners exposed to
dpm.
During the hearings and in written comments, some representatives
of the mining industry raised a number of objections to parts of MSHA's
proposed risk assessment, thus questioning the scientific basis for
this rulemaking. It has been asserted that MSHA's observations of dpm
concentrations in underground metal and nonmetal mines do not
accurately represent exposures in the industry. It has been asserted
that if dpm concentrations are not this high in general, or only on an
intermittent basis, then the agency is incorrect in determining that
the conditions in these mines put miners at significant risk of
material impairment of their health. Moreover it has been asserted that
there is insufficient evidence to establish a causal connection between
dpm exposure and significant adverse health effects, that the agency
has no hard evidence that reducing exposures to a particular level will
in fact reduce the risks, and that it has no rational basis for
selecting the concentration limit it did. In addition, it has been
asserted that the risks of dpm exposure at any level are not well
enough established to provide the basis for regulation at this time,
and that action should be postponed pending the completion of various
studies now underway that might shed more light on these risks.
MSHA has carefully evaluated all of these comments, and the
evidence submitted in support of these positions. The agency's risk
assessment has been modified as a result.
Exposures of underground metal and nonmetal miners. MSHA has
clarified the charts of exposure measurements in Part III of this
preamble to ensure that they fully reflect all studies in the record.
MSHA has not and does not claim that the actual exposure
measurements in the record are a random or fully representative sample
of the industry. What they do show is that exposures far higher than
those which have been observed in other industries can and do occur in
an underground mining environment.
Moreover, MSHA also placed into the record of the proposed rule
several studies it had recently conducted in which dpm concentrations
for several underground metal and nonmetal mines were estimated based
upon the actual equipment and dpm controls currently available in those
mines. Those simulations were performed using a software tool known as
the Estimator (described in detail in an appendix to Part V of the
preamble of the proposed rule, and since published in the literature
(Haney and Saseen, April 2000). These studies of specific mines
demonstrated that the type of equipment found in such mines, even after
the application of current ventilation and controls, can be expected to
produce localized high concentrations of dpm. The agency acknowledged
that these simulations were conducted in mines that were not typical
for the industry (they were chosen because the agency thought dpm
concentrations might be particularly difficult to control in these
mines, which turned out not to be the case); nevertheless, they
indicate what is likely to be the case in at least some sections of
many underground metal and nonmetal mines. To the extent that an
individual mine has no covered mining areas with concentrations higher
than those observed in other industries, it will not be impacted by the
concentration limit established through this rulemaking. That is
because the rule does not eliminate exposures, or even to reduce them
to a safe level, but only to reduce them to the levels observed in
other industries.
The nature of risks associated with dpm exposure. Although there
were some commenters who suggested that symptoms reported by miners
working around diesel equipment might be due to the gases present
rather than dpm, there was nothing in the comments that changed MSHA's
conclusions about the health problems associated with dpm exposure.
There are a number of studies quantifying significant adverse
health effects--as measured by lost work days, hospitalization and
increased mortality rates--suffered by the general public when exposed
to concentrations of fine particulate matter like dpm far lower than
concentrations to which some miners are exposed. The evidence from
these fine particulate studies was the basis for recent rulemaking by
the Environmental Protection Agency \1\ to further restrict the
exposure of the general public to fine particulates, and the evidence
was given very widespread and close scrutiny before that action was
made final. Of particular interest to the mining community is that
these fine particulate studies indicate that smokers and those who have
pre-existing pulmonary problems are particularly at risk. Many
individual miners in fact have such pulmonary problems and are
especially susceptible to the adverse health effects of inhaling fine
particles.
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\1\ The basis for the PM2.5 NAAQS was a large body of
scientific data indicating that particles in this size range are
responsible for the most serious health effects associated with
particulate matter. The evidence was thoroughly reviewed by a number
of scientific panels through an extended process. The proposed rule
resulted in considerable public attention, and hearings by Congress,
in which the scientific evidence was further discussed. Moreover,
challenges to the EPA's determination that this size category
warranted rulemaking were rejected by a three-judge panel of the DC
Circuit Court. (ATA v. EPA, 175 F.3d 1027, D.C. Circuit 1999).
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Although no epidemiological study is flawless, numerous
epidemiological studies have shown that long term exposure to diesel
exhaust in a variety of occupational circumstances is associated with
an increased risk of lung cancer. With only rare exceptions, involving
relatively few workers and/or observation periods too short to reliably
detect excess cancer risk, the human studies have consistently shown a
greater risk of lung cancer among workers exposed to dpm than among
comparable unexposed workers. When results from the human studies are
combined, the risk is estimated to be 30-40 percent greater among
exposed workers, if all other factors (such as smoking habits) are held
constant. The consistency of the human study results, supported by
experimental data establishing the plausibility of a causal connection,
provides strong evidence that chronic dpm exposure at high levels
significantly increases the risk of lung cancer in humans.
Moreover, all of the occupational studies indicating an increased
frequency of lung cancer among workers exposed to dpm involved exposure
levels estimated, on average, to be far below levels observed in
underground mines. Except for miners, the workers
[[Page 5710]]
included in these studies were exposed to average dpm levels below the
limit established by this rule.
As noted in Part III, MSHA views extrapolations from animal
experiments as subordinate to results obtained from human studies.
However, it is noteworthy that dpm exposure levels recorded in some
underground mines have been of the same order of magnitude that
produced tumors in rats.
Based on the scientific data available in 1988, the National
Institute for Occupational Safety and Health (NIOSH) identified dpm as
a probable or potential human carcinogen and recommended that it be
controlled. Other organizations have made similar recommendations. Most
recently, the National Toxicology Program listed dpm as ``reasonably
anticipated to be a human carcinogen'' in the Ninth Edition (Year 2000)
of the National Report on Carcinogens.
The relationship between exposures and risks. Commenters noted
MSHA's caution about trying to define a quantitative relationship
between dpm exposure and particular health outcomes. They roundly
attacked the agency's benefit analysis and a NIOSH paper reviewing
quantification efforts as implying that such a relationship could be
established in a valid way.
As MSHA acknowledged in the preamble to the proposed rule, the
scientific community has not yet widely accepted any exposure-response
relationship between the amount of dpm exposure and the likelihood of
adverse health outcomes (63FR 58167). There are, however, two lung
cancer studies in the record that show increasing risk of lung cancer
with increasing levels of dpm exposure. Quantitative results from these
studies, both conducted specifically on underground miners, can be used
to estimate the reduction in lung cancer risk expected when dpm
exposure is reduced in accordance with this rule. Depending on the
study and method of statistical analysis used, these estimates range
from 68 to 620 lung cancer deaths prevented, over an initial 65-year
period, per 1000 affected miners with lifetime (45-year) exposure to
dpm.
NIOSH and the National Cancer Institute (NCI) are collaborating on
a cancer mortality study designed to provide additional information in
this regard. The study is projected to take about seven years.
Notwithstanding this situation, MSHA believes the Agency is
required under its statute to take action now to protect miners'
health. As noted by the Supreme Court in an important case on risk
involving the Occupational Safety and Health Administration, the need
to evaluate risk does not mean an agency is placed into a
``mathematical straightjacket.'' Industrial Union Department, AFL-CIO
v. American Petroleum Institute, 448 U.S. 607, 100 S.Ct. 2844 (1980).
The Court noted that when regulating on the edge of scientific
knowledge, absolute scientific certainty may not be possible, and:
so long as they are supported by a body of reputable scientific
thought, the Agency is free to use conservative assumptions in
interpreting the data * * * risking error on the side of
overprotection rather than underprotection. (Id. at 656).
This advice has special significance for the mining community, because
a singular historical factor behind the enactment of the current Mine
Act was the slowness of the mining community in coming to grips with
the harmful effects of other respirable dust (coal dust).
It is worth noting that while the cohort selected for the NIOSH/NCI
study consists of underground miners (specifically, underground metal
and nonmetal miners), this choice is in no way linked to MSHA's
regulatory framework or to miners in particular. This cohort was
selected for the study because it provides the best population for
scientists to study. For example, one part of the study would compare
the health experiences of miners who have worked underground in mines
with long histories of diesel use with the health experiences of
similar miners who work in surface areas where exposure is
significantly lower. Since the general health of these two groups is
very similar, this will help researchers to quantify the impacts of
diesel exposure. No other population is likely to be as easy to study
for this purpose. But as with any such epidemiological study, the
insights gained are not limited to the specific population used in the
study. Rather, the study will provide information about the
relationship between exposure and health effects that will be useful in
assessing the risks to any group of workers in a dieselized industry.
Because of the lack of a generally accepted dose-response
relationship, some commenters questioned the agency's rationale in
picking a particular concentration limit: 160TC g/
m3 or around 200DPM g/m3.
Capping dpm concentrations at this level will eliminate the worst
mining exposures, and bring miner exposures down to a level
commensurate with those reported for other groups of workers who use
diesel-powered equipment. The proposed rule would not bring
concentrations down as far as the proposed ACGIH TLVR of
150DPM g/m3. Nor does MSHA's risk
assessment suggest that the proposed rule would completely eliminate
the significant risks to miners of dpm exposure.
In setting the concentration limit at this particular value, the
Agency is acting in accord with its statutory obligation to attain the
highest degree of safety and health protection for miners that is
feasible. The Agency's risk assessment supports reduction of dpm to the
lowest level possible. But feasibility considerations dictated
proposing a concentration limit that does not completely eliminate the
significant risks that dpm exposure poses to miners.
The Agency specifically explored the implications of requiring
mines in this sector to comply with a lower concentration limit than
that being adopted. The results, discussed in Part V of this preamble,
indicate that although the matter is not free from question, it still
may not be feasible at this time for the underground metal and nonmetal
mining industry as a whole to comply with a significantly lower limit
than that being adopted. The Agency notes that since this rulemaking
was initiated, the efficiency of hot gas filters has improved
significantly, the dpm emissions from new engines continue to decline
under EPA requirements, and the availability of ultra-low sulfur fuel
should make controls even more efficient than at present.
The agency also explored the idea of bridging the gap between risk
and feasibility by establishing an ``action level''. In the case of
MSHA's noise rule, for example, MSHA adopted a ``permissible exposure
level'' of a time-weighted 8-hour average (TWA8) of 90 dBA
(decibels, A-weighted), and an ``action level'' of half that amount--a
TWA8 of 85 dBA. In that case, MSHA determined that miners
are at significant risk of material harm at a TWA8 of 85
dBA, but technological and feasibility considerations preclude the
industry as a whole, at this time, below a TWA8 of 90 dBA.
Accordingly, to limit miner exposure to noise at or above a
TWA8 of 85 dBA, MSHA requires that mine operators must take
certain actions that are feasible (e.g., provide hearing protectors).
MSHA considered the establishment of a similar ``action level'' for
dpm--probably at half the proposed concentration limit, or
80TC g/m3. Under such an approach, mine
operators whose dpm concentrations are above the ``action level'' would
be required to implement a series of ``best practices''--e.g., limits
on fuel types,
[[Page 5711]]
idling, and engine maintenance. Only one commenter supported the
creation of an Action Level for dpm. However, this commenter suggested
that such an Action Level be adopted in lieu of a rule incorporating a
concentration limit requiring mandatory compliance. The agency
determined it is feasible for the entire underground mining community
to implement these best practices to minimize the risks of dpm exposure
without the need for a trigger at an Action Level.
Some of the comments suggesting that the agency had no rational
basis for setting the exposure limit at 160TC g/
m3 seem to suggest that the statute itself does not provide
the Agency with adequate guidance in this regard. The Agency recognizes
that the Supreme Court has scheduled argument on a case that raises the
question of how specific a regulatory statute must be with respect to
how an agency must make standards determinations in order to be deemed
a constitutional delegation of authority from the Congress. A decision
is not expected until 2001. However, unless and until determined
otherwise, MSHA presumes the Mine Act does pass constitutional muster
in this regard, consistent with the existing case law concerning the
very similar Occupational Safety and Health Act.
(B) The ability of the agency to accurately measure diesel
particulate matter (dpm) in underground metal and nonmetal mine
environments. As MSHA noted in the preamble to the proposed rule, there
are a number of methods which can measure dpm concentrations with
reasonable accuracy when it is at high concentrations and when the
purpose is exposure assessment. Measurements for the purpose of
compliance determinations must be more accurate, especially if they are
to measure compliance with a dpm concentration of 200DPM
g/m3 or lower. Accordingly, MSHA noted that it
needed to address a number of questions as to whether such any existing
method could produce accurate, reliable and reproducible results in the
full variety of underground mines, and whether the infrastructure
(samplers and laboratories) existed to support such determinations.
(See 63 FR 58127 et seq.).
MSHA concluded that there was no method suitable for such
compliance measurements in underground coal mines, due to the inability
of the available methods to distinguish between dpm and coal dust.
Accordingly, the agency developed a rule for the coal mining sector
that does not depend upon ambient dpm measurements.
By contrast, the agency tentatively concluded that by using a
sampler developed by the Bureau of Mines, and an analytical method
developed by the National Institute for Occupational Safety and Health
(NIOSH) to detect the total amount of carbon in a sample, MSHA could
accurately measure dpm levels at the required concentrations in
underground metal and nonmetal mines. While not requiring operators to
use this method for their own sampling, MSHA did commit itself through
provisions of the proposed rule to use this approach (or a method
subsequently determined by NIOSH to provide equal or improved accuracy)
for its own sampling. Moreover the agency proposed that MSHA sampling
be the sole basis upon which determinations would be made of compliance
by metal and nonmetal mine operators with applicable compliance limits,
and that a single sample would be adequate for such purposes.
Specifically, proposed Sec. 57.5061 provided as follows:
Sec. 57.5061 Compliance Determinations
(a) A single sample collected and analyzed by the Secretary in
accordance with the procedure set forth in paragraph (b) of this
section shall be an adequate basis for a determination of
noncompliance with an applicable limit on the concentration of
diesel particulate matter pursuant to Sec. 57.5060.
(b) The Secretary will collect and analyze samples of diesel
particulate matter by using the method described in NIOSH Analytical
Method 5040 and determining the amount of total carbon, or by using
any method subsequently determined by NIOSH to provide equal or
improved accuracy in mines subject to this part.
This part of MSHA's proposed rule received considerable comment.
Some commenters challenged the accuracy, precision and sensitivity of
NIOSH Analytical Method 5040. Some challenged whether the amount of
total carbon determined by the method is a reliable way to determine
the amount of dpm. Others questioned whether the sampler developed by
the Bureau of Mines would provide an accurate sample to be analyzed,
and whether such samplers and analytical procedures would be
commercially available. Commenters also questioned the use of a single
sample as the basis for a compliance determination, and the use of area
sampling in compliance determinations. These comments are addressed
elsewhere in this preamble (section 3 of Part II, and in connection
with section 5061 in Part IV).
Here, MSHA summarizes its views on the most common assertion made
by commenters: that the sampling and analytical methods the agency
proposed to use are not able to distinguish between dpm and various
other substances in the atmosphere of underground metal and nonmetal
mines--carbonates and carbonaceous minerals, graphitic materials, oil
mists and organic vapors, and cigarette smoke.
Interferences: what MSHA said in preamble to proposed rule. In the
preamble to the proposed rule, MSHA recognized that there might be some
interferences from other common organic carbon sources in underground
metal and nonmetal mines: specifically, oil mists and cigarette smoke.
The agency noted it had no data on oil mists, but had not encountered
the problem in its own sampling. With respect to cigarette smoke, the
agency noted that: ``Cigarette smoke is under the control of operators,
during sampling times in particular, and hence should not be a
consideration.'' (63FR 58129)
The agency also discussed the potential advantages and
disadvantages of using a special device on the sampler--a submicron
impactor--to eliminate certain other possible interferences (See Figure
I-1). The submicron impactor stops particles larger than a micron from
being collected by the sampler, while allowing the smaller dpm to be
collected. Thus, an advantage of using the impactor would be to ensure
that the sampler was not inadvertently collecting materials other than
dpm. However MSHA pointed out that while samples in underground metal
and nonmetal mines could be taken with a submicrometer impactor, this
could lead to underestimating the total amount of dpm present (63FR
58129). This is because the fraction of dpm particles greater than 1
micron in size in the environment of noncoal mines can be as great as
20% (Vuk, Jones, and Johnson, 1976).
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Interferences: comments and MSHA efforts to verify. Many commenters
asserted that no matter how it is performed in underground metal and
nonmetal mines, the sampling and analysis proposed by MSHA to determine
the amount of diesel particulate present would suffer from one or more
of the aforementioned interferences. A number asserted that their own
measurements using this approach provided clear evidence of such
interferences. Although MSHA repeatedly asked for actual data and
information about the procedures used to verify these assertions, very
little was provided. Nevertheless, rather than conclude that these
assertions were baseless, MSHA decided to attempt to verify these
assertions itself. Accordingly, appropriate field and laboratory
measurements were conducted toward this end, the results written up in
appropriate fashion, and added to the record of this rulemaking. The
agency has taken those results into account in ascertaining what weight
to give to the assertions made by commenters and how to deal with those
assertions supported by its measurements.
As described in detail in section 3 of Part II, MSHA's
verifications demonstrate that the submicron impactor can eliminate any
interferences from carbonates, carbonaceous minerals, and graphitic
ores. Accordingly, although use of the impactor will result in an
undercount of dpm, the final rule provides that MSHA will always use
the submicron impactor in compliance sampling.
MSHA's verifications also demonstrated that oil mists as well as
cigarette smoke, can in fact, under certain circumstances, create
interferences even with the use of the impactor. MSHA presumes the same
would happen with organic vapors. The verifications demonstrated that
the problems occur in the immediate vicinity of the interferent (e.g.,
close to a drill or smoker). However, the verifications also
demonstrated that the interference dissipates when the sampling device
is located a certain distance away from the interferent.
Accordingly, as detailed in the discussion of section 5061 in Part
IV of this preamble, MSHA's sampling strategy for dpm will take these
problems into account. For example, if a miner works in an enclosed cab
all day and smokes, MSHA will not place a sampler in that cab or on
that miner. If a miner works part of a day drilling, MSHA will not
place a sampler on that miner. But MSHA can, for example, take an area
sample in an area of a mine where drilling is being performed without
concern about interferences from oil mists if it locates the sampler
far enough away from the drill. MSHA's compliance manual will provide
specific instructions to inspectors on how to avoid interferences.
The organic interferences (diesel mist, smoking) could be avoided
by only analyzing a sample for elemental carbon, pursuant to the NIOSH
method. As it indicated in the preamble to the proposed rule, however,
MSHA does not at this time know the ratio between the amount of
elemental carbon and the amount of dpm. Accordingly, rather than deal
with the uncertainties in all samples which this approach would
present, MSHA is going to use a method (i.e., sampling and analyzing
for both organic carbon and elemental carbon) that, if properly
applied, provides accurate results.
(C) The feasibility of the requirements for this sector of the
mining industry. The Mine Act generally requires MSHA to set the
standard that is most protective of miner health while still being
technologically and economically feasible. In addition, consistent with
the Regulatory Flexibility Act, the agency pays particular attention to
the impact of any standard on small mining operations.
(1) Technological feasibility of the rule. It has been clear since
the beginning of this rulemaking that if technological feasibility was
an issue, it would be in the context of requiring all underground metal
and nonmetal mines to meet a particular limit. While the Mine Act does
not require that each mine be able to meet a standard for it to be
considered technologically feasible--only that the standard be feasible
for the industry as a whole--the extent to which various mines might
have a problem complying is the evidence upon which this conclusion
must be based.
Accordingly, MSHA evaluated the technological feasibility of the
concentration limit in the underground
[[Page 5713]]
metal and nonmetal sector by evaluating whether it was possible, using
a combination of existing control approaches, to reach the
concentration limit even in situations in which the Agency's engineers
determined that compliance might be the most difficult. In this regard,
the Agency examined how emissions generated by the actual equipment in
four different underground mining operations could be controlled. The
mines were very diverse--an underground limestone mine, an underground
(and underwater) salt mine, and an underground gold mine. Yet in each
case, the analysis revealed that there are available combinations of
controls that can bring dpm concentrations down to well below the final
limit--even when the controls that needed to be purchased were not as
extensive as those which the Agency is assuming will be needed in
determining the costs of the final rule. (The results of these analyses
are discussed in Part V of the preamble, together with the methodology
used in modeling the results--just as they were discussed in the
preamble accompanying the proposed rule.) As a result of these studies,
the Agency has concluded that there are engineering and work practice
controls available to bring dpm concentrations in all underground metal
and nonmetal mines down to the required levels.
The best actions for an individual operator to take to come into
compliance with the interim and final concentration limits will depend
upon an analysis of the unique conditions at the mine. The final rule
provides 18 months after it is promulgated for MSHA to provide
technical assistance to individual mine operators. It also gives all
mine operators in this sector an additional three and a half years to
bring dpm concentrations down to the proposed final concentration
limit--using an interim concentration limit during this time which the
Agency is confident every mine in this sector can timely meet. And the
rule provides an opportunity for a special extension for an additional
two years for mines that have unique technological problems meeting the
final concentration limit.
As noted during 1995 workshops co-sponsored by MSHA on methods for
controlling diesel particulate, many underground metal and nonmetal
mine operators have already successfully determined how to reduce
diesel particulate concentrations in their mines. MSHA has disseminated
the ideas discussed at these workshops to the entire mining community
in a publication, ``Practical Ways to Control Exposure to Diesel
Exhaust in Mining--a Toolbox''. The control methods are divided into
eight categories: use of low emission engines; use of low sulfur fuel;
use of aftertreatment devices; use of ventilation; use of enclosed
cabs; diesel engine maintenance; work practices and training; fleet
management; and respiratory protective equipment. Moreover, MSHA
designed a model in the form of a computer spreadsheet that can be used
to simulate the effects of various controls on dpm concentrations.
(This model is discussed in Part V of the preamble.) This makes it
possible for individual underground mine operators to evaluate the
impact on diesel particulate levels of various combinations of control
methods, prior to making any investments, so each can select the most
feasible approach for his or her mine.
(2) Economic Feasability of the Rule. The underground metal and
nonmetal industry uses a lot of diesel-powered equipment, and it is
widely distributed. Accordingly, MSHA recognizes that the costs of
bringing mines into compliance with this rule will be widely felt in
this sector (although, unlike underground coal mines, this sector did
not have to comply with MSHA's 1996 diesel equipment rule).
In summary, the costs per year to the underground metal and
nonmetal industry are about $25.1 million. The cost for an average
underground metal and nonmetal mine is expected to be about $128,000
annually.
The Agency's initial cost estimates of $19.2 million a year were
challenged during the rulemaking proceeding. As a result, the Agency
reconsidered the costs.
In its initial estimate of the costs for the industry to comply
with the concentration limit, MSHA assumed that a variety of
engineering controls, such as low emission engines, ceramic filters,
oxidation catalytic converters, and cabs would be needed on diesel
powered equipment. Most of the engineering controls would be needed on
diesel equipment used for production, while a small amount of diesel
equipment that is used for support purposes would need engineering
controls. In addition to these controls, MSHA assumed that some
underground metal and nonmetal mines would need to make ventilation
changes in order to meet the proposed concentration limits.
Specifically, in the PREA, MSHA assumed that: (1) the interim
standard would be met by replacing engines, installing oxidation
catalytic converters, and improving ventilation; and (2) the final
standard would be met by adding cabs and filters. Comments on the PREA
and data collected by the Agency since publication of the proposed rule
indicate that engine replacement is more expensive than originally
thought and filters are more effective relative to engine replacement.
The revised compliance strategy, upon which MSHA bases its revised
estimates of compliance costs, reverses the two most widely used
measures. MSHA now anticipates that: (1) the interim standard will be
met with filters, cabs, and ventilation; and (2) the final standard
will be met with more filters, ventilation, and such turnover in
equipment and engines as will have occurred in the baseline. This new
approach uses the same toolbox and optimization strategy that was used
in the PREA. Since relative costs are different, however, the tools
used and cost estimated are different.
(3) Impact on small mines. As required by the Regulatory
Flexibility Act, MSHA has performed a review of the effects of the
proposed rule on ``small entities''.
The Small Business Administration generally considers a small
mining entity to be one with less than 500 employees. MSHA has
traditionally defined a small mine to be one with less than 20 miners,
and has focused special attention on the problems experienced by such
mines in implementing safety and health rules. Accordingly, MSHA has
separately analyzed the impact of the rule on three categories of
mines: large mines (more than 500 employees), middle size mines (20-500
employees), and small mines (those with less than 20 miners).
As required by law, MSHA has also developed a preliminary and final
regulatory flexibility analysis. The Agency published its preliminary
Regulatory Flexibility Analysis with its proposed rule and specifically
requested comments thereon; the agency's final Regulatory Flexibility
Analysis is included in the Agency's REA. In addition to a succinct
statement of the objectives of the rule and other information required
by the Regulatory Flexibility Act, the analysis reviews alternatives
considered by the Agency with an eye toward the nature of small
business entities.
In promulgating standards, MSHA is required to protect the health
and safety of all the Nation's miners and may not include provisions
that provide less protection for miners in small mines than for those
in larger mines. But MSHA does consider the impact of its standards on
even the smallest mines when it evaluates the feasibility of various
alternatives. For example, a major reason why MSHA concluded it
[[Page 5714]]
needed to stagger the effective dates of some of the requirements in
the rule is to ensure that it would be feasible for the smallest mines
to have adequate time to come into compliance.
MSHA recognizes that smaller mines may need particular assistance
from the agency in coming into compliance with this standard. Before
the dpm concentration goes into effect in 18 months, the Agency plans
to provide extensive compliance assistance to the mining community. The
metal and nonmetal community will also have an additional three and a
half years to comply with the final concentration limit, which in many
cases means these mines may have a full five years of technical
assistance before any engineering controls are required. MSHA intends
to focus its efforts on smaller operators in particular--training them
in measuring dpm concentrations, and providing technical assistance on
available controls. The Agency will also issue a compliance guide, and
continue its current efforts to disseminate educational materials and
software.
(4) Benefits of the final rule Benefits of the rule include
reductions in lung cancer. In the long run, as the mining population
turns over, MSHA estimates that a minimum of 8.5 lung cancer deaths
will be avoided per year.\2\
---------------------------------------------------------------------------
\2\ This lower bound figure could significantly underestimate
the magnitude of the health benefits. For example the estimate based
on the mean value of all the studies examined is 49 lung cancer
deaths avoided per year.
---------------------------------------------------------------------------
Benefits of the rule will also include reductions in the risk of
death from cardiovascular, cardiopulmonary, or respiratory causes and
in sensory irritation and respiratory symptoms. MSHA does not believe
that the available data can support reliable or precise quantitative
estimates of these benefits. Nevertheless, the expected reductions in
the risk of death from cardiovascular, cardiopulmonary, or respiratory
causes appear to be significant, and the expected reductions in sensory
irritation and respiratory symptoms appear to be rather large.
II. General Information
This part provides the context for this preamble. The nine topics
covered are:
(1) The role of diesel-powered equipment in underground metal and
nonmetal mining in the United States;
(2) The composition of diesel exhaust and diesel particulate matter
(dpm);
(3) The sampling and analytical techniques for measuring ambient
dpm in underground metal and nonmetal mines;
(4) Limiting the public's exposure to diesel and other final
particulates-- ambient air quality standards;
(5) The effects of existing standards--MSHA standards on diesel
exhaust gases (CO, CO2, NO, NO2, and
SO2), and EPA diesel engine emission standards--on the
concentration of dpm in underground metal and nonmetal mines;
(6) Methods for controlling dpm concentrations in underground metal
and nonmetal mines;
(7) MSHA's approach to diesel safety and health in underground coal
mines and its effect on dpm;
(8) Information on how certain states are restricting occupational
exposure to dpm; and
(9) A history of this rulemaking.
Material on these subjects which was available to MSHA at the time
of the proposed rulemaking was included in Part II of the preamble that
accompanied the proposed rule. (63 FR 58123 et seq). Portions of that
material relevant to underground metal and nonmetal mines is reiterated
here (although somewhat reorganized), and the material is amended and
supplemented where appropriate as a result of comments and additional
information added to the record since the proposal was published.
(1) The Role of Diesel-Powered Equipment in Underground Metal and
Nonmetal Mining in the United States
Diesel engines, first developed about a century ago, now power a
full range of mining equipment in underground metal and nonmetal mines,
and are used extensively in this sector. This sector's reliance upon
diesel engines to power equipment in underground metal and nonmetal
mines appears likely to continue for some time.
Historical Overview of Diesel Power Use in Mining. As discussed in
the notice of proposed rulemaking, the diesel engine was developed in
1892 by the German engineer Rudolph Diesel. It was originally intended
to burn coal dust with high thermodynamic efficiency. Later, the diesel
engine was modified to burn middle distillate petroleum (diesel fuel).
In diesel engines, liquid fuel droplets are injected into a prechamber
or directly into the cylinder of the engine. Due to compression of air
in the cylinder the temperature rises high enough in the cylinder to
ignite the fuel.
The first diesel engines were not suited for many tasks because
they were too large and heavy (weighing 450 lbs. per horsepower). It
was not until the 1920's that the diesel engine became an efficient
lightweight power unit. Since diesel engines were built ruggedly and
had few operational failures, they were used in the military, railway,
farm, construction, trucking, and busing industries. The U.S. mining
industry was slow, however, to begin using these engines. Thus, when in
1935 the former U.S. Bureau of Mines published a comprehensive overview
on metal mine ventilation (McElroy, 1935), it did not even mention
ventilation requirements for diesel-powered equipment. By contrast, the
European mining community began using these engines in significant
numbers, and various reports on the subject were published during the
1930's. According to a 1936 summary of these reports (Rice, 1936), the
diesel engine had been introduced into German mines by 1927. By 1936,
diesel engines were used extensively in coal mines in Germany, France,
Belgium and Great Britain. Diesel engines were also used in potash,
iron and other mines in Europe. Their primary use was in locomotives
for hauling material.
It was not until 1939 that the first diesel engine was used in the
United States mining industry, when a diesel haulage truck was used in
a limestone mine in Pennsylvania, and not until 1946 was a diesel
engine used in a coal mine. Today, however, diesel engines are used to
power a wide variety of equipment in all sectors of U.S. mining.
Production equipment includes vehicles such as haultrucks and shuttle
cars, front-end loaders, hydraulic shovels, load-haul-dump units, face
drills, and explosives trucks. Diesel engines are also used in support
equipment including generators and air compressors, ambulances, fire
trucks, crane trucks, ditch diggers, forklifts, graders, locomotives,
lube units, personnel carriers, hydraulic power units, longwall
component carriers, scalers, bull dozers, pumps (fixed, mobile and
portable), roof drills, elevating work platforms, tractors, utility
trucks, water spray units and welders.
Current Patterns of Diesel Power Use in Underground Metal and
Nonmetal Mining. Table II-1 provides information on the current
utilization of diesel equipment in underground metal and nonmetal
mines.
[[Page 5715]]
Table II-1.--Diesel Equipment in Underground Metal and Nonmetal Mines
----------------------------------------------------------------------------------------------------------------
Number of
Mine size underground mines Number of mines Number of Engines
A with diesels B B
----------------------------------------------------------------------------------------------------------------
Small C................................................ 134 77 584
Large.................................................. 130 119 3,414
All.................................................... 264 196 3,998
----------------------------------------------------------------------------------------------------------------
(A) Number of underground mines is based on those reporting operations for FY1999 (preliminary data).
(B) Number of mines using diesels are based on January 1998 count, by MSHA inspectors, of underground metal and
nonmetal mines that used diesel powered equipment, and the number of engines (the latter rounded to the
nearest 25) was determined in the same count with reference to equipment normally in use.
(C) A ``small'' mine is one with less than 20 miners.
As noted in Table II-1, a majority of underground metal and
nonmetal mines use diesel-powered equipment.
Diesel engines in metal and nonmetal underground mines, and in
surface coal mines, range up to 750 HP or greater, although equipment
size, and thus the size of the engine, can be limited by production
requirements, the dimensions of mine openings, and other factors. By
contrast, in underground coal mines, the average engine size is less
than 150 HP. The reason for this disparity is the nature of the
equipment powered by diesel engines. In underground metal and nonmetal
mines, and surface mines, diesel engines are widely used in all types
of equipment--both the equipment used under the heavy stresses of
production and the equipment used for support. In underground metal and
nonmetal mines, of the approximate 4,000 pieces of diesel equipment
normally in use, about 1,800 units are used for loading and hauling. By
contrast, the great majority of the diesel usage in underground coal
mines is in support equipment.
This fact is significant for dpm control in underground metal and
nonmetal mines. As the horsepower size of the engine increases, the
mass of dpm emissions produced per hour increases. (A smaller engine
may produce the same or higher levels of particulate emissions per
volume of exhaust as a large engine, but the mass of particulate matter
increases with the engine size). Accordingly, as engine size increases,
control of emissions may require additional efforts.
Another factor relevant to control of dpm emissions in this sector
is that fewer than 15 underground metal and nonmetal mines are required
to use Part 36 permissible equipment because of the possibility of the
presence of explosive mixtures of methane and air. The surface
temperature of diesel powered equipment in underground metal and
nonmetal mines classified as gassy must be controlled to less than
400 deg.F. Such mines must use equipment approved as permissible under
Part 36 if the equipment is utilized in areas where permissible
equipment is required. These gassy metal and nonmetal mines have been
using the same permissible engines and power packages as those approved
for underground coal mines. (MSHA has not certified a diesel engine
exclusively for a Part 36 permissible machine for the metal and
nonmetal sector since 1985 and has certified only one permissible power
package; however, that engine model has been retired and is no longer
available as a new purchase to the industry). As a result, engine size
(and thus dpm production of each engine) is more limited in these
mines, and, as explained in section 6 of this part, the exhaust from
these engines is cool enough to add a paper type of filtration device
directly to the equipment.
By contrast, since in nongassy underground metal and nonmetal mines
mine operators can use conventional construction equipment in their
production sections without the need for modifications to the machines,
they tend to do so. Two examples are haulage vehicles and front-end
loaders. As a result, these mines can and do use engines with larger
horsepower and hot exhaust. As explained in section 6 of this part, the
exhaust from such engines must be cooled by a wet or dry device before
a paper filter can be used, or high temperature filters (e.g.,
ceramics) must be used.
At this time, diesel power faces little competition from other
power sources in underground metal and nonmetal mines. As can be seen
from the chart, there are some small metal and nonmetal mines (less
than 20 employees) which do not use diesel-powered equipment; most of
these used compressed air for drilling and battery-powered rail
equipment for haulage.
It is unclear at this time, how quickly new ways to generate energy
to run mobile vehicles will be available for use in a wide range of
underground metal and nonmetal mining activities. New hybrid electric
automobiles are being introduced this year by two manufacturers (Honda
and Toyota); such vehicles combine traditional internal combustion
power sources (in this case gasoline) with electric storage and
generating devices that can take over during part of the operating
period. By reducing the time the vehicle is directly powered by
combustion, such vehicles reduce emissions. Further developments in
electric storage devices (batteries), and chemical systems that
generate electricity (fuel cells) are being encouraged by government-
private sector partnerships. For further information on recent
developments, see the Department of Energy alternative fuels web site
at http://www.afdc.doe.gov/altfuels.html, and ``The Future of Fuel
Cells'' in the July 1999 issue of Scientific American. Until such new
technologies mature, are available for use in large equipment, and are
reviewed for safe use underground, however, MSHA assumes that the
underground metal and nonmetal mining community's significant reliance
upon the use of diesel-power will continue.
(2) The Composition of Diesel Exhaust and Diesel Particulate Matter
(DPM)
The emissions from diesel engines are actually a complex mixture of
compounds, containing gaseous and particulate fractions. The specific
composition of the diesel exhaust in a mine will vary with the type of
engines being used and how they are used. Factors such as type of fuel,
load cycle, engine maintenance, tuning, and exhaust treatment will
affect the composition of both the gaseous and particulate fractions of
the exhaust. This complexity is compounded by the multitude of
environmental settings in which diesel-powered equipment is operated.
Nevertheless, there are a few basic facts about diesel emissions that
are of general applicability.
The gaseous constituents of diesel exhaust include oxides of
carbon, nitrogen and sulfur, alkanes and alkenes (e.g., butadiene),
aldehydes (e.g., formaldehyde), monocyclic aromatics (e.g., benzene,
toluene), and polycyclic aromatic hydrocarbons (e.g.,
[[Page 5716]]
phenanthrene, fluoranthene). The oxides of nitrogen ( NOX)
are worth particular mention because in the atmosphere they can
precipitate into particulate matter. Thus, controlling the emissions of
NOX is one way that engine manufacturers can control
particulate production indirectly. (See section 5 of this part).
The particulate components of the diesel exhaust gas include the
so-called diesel soot and solid aerosols such as ash particulates,
metallic abrasion particles, sulfates and silicates. The vast majority
of these particulates are in the invisible sub-micron range of 100nm.
The main particulate fraction of diesel exhaust is made up of very
small individual particles. These particles have a solid core mainly
consisting of elemental carbon. They also have a very surface-rich
morphology. This surface absorbs many other toxic substances, that are
transported with the particulates, and can penetrate deep into the
lungs. There can be up to 1,800 different organic compounds adsorbed
onto the elemental carbon core. A portion of this hydrocarbon material
is the result of incomplete combustion of fuel; however, the majority
is derived from the engine lube oil. In addition, the diesel particles
contain a fraction of non-organic adsorbed materials. Figure II-1
illustrates the composition of dpm.
Diesel particles released to the atmosphere can be in the form of
individual particles or chain aggregates (Vuk, Jones, and Johnson,
1976). In underground coal mines, more than 90% of these particles and
chain aggregates are submicrometer in size (i.e., less than 1
micrometer (1 micron) in diameter). Dust generated by mining and
crushing of material--e.g., silica dust, coal dust, rock dust--is
generally not submicrometer in size. Figure II-2 shows a typical size
distribution of the particles found in the environment of a mine that
uses equipment powered by diesel engines (Cantrell and Rubow, 1992).
The vertical axis represents relative concentration, and the horizontal
axis the particle diameter. As can be seen, the distribution is
bimodal, with dpm generally being well less than 1 m in size
and dust generated by the mining process being well greater than 1
m.
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As shown on Figure II-3 (Majewski, W. Addy, Diesel Progress June,
1998) diesel particulates have a bimodal size distribution which
includes small nuclei mode particles and larger accumulation mode
particles. As further shown, most of diesel particle mass is contained
in the accumulation mode but most of the particle number can be found
in the nuclei mode.
The particles in the nuclei mode, also known as nanoparticles, are
being investigated as to their health hazard relevance. The interest in
these particles has been sparked by the finding that newer ``low
polluting engines emit higher numbers of small particles than the old
technology engines. Although the exact composition of diesel
nanoparticles is not known, it was found that they may be composed of
condensates (hydrocarbons, water, sulfuric acid). The amount of these
condensates and the number of nanoparticles depends very significantly
on the particulate sampling conditions, such as dilution ratios, which
were applied during the measurement.
Both the maximum particle concentration and the position of the
nuclei and accumulation mode peaks, however, depend on which
representation is chosen. In mass distributions, the majority of the
particulates (i.e., the particulate mass) is found in the accumulation
mode. The nuclei mode, depending on the engine technology and particle
sampling technique, may be as low as a few percent, sometimes even less
than 1%. A different picture is presented when the number distribution
representation is used. Generally, the number of particles in the
nuclei mode contributes to more than 50% of the total particle count.
However, sometimes the nuclei mode particles represent as much as 99%
of the total particulate number. The topic of nanoparticles is
discussed further in section 5 of this Part.
(3) The Sampling and Analytical Techniques for Measuring Ambient dpm in
Underground Metal and Nonmetal Mines
As MSHA noted in the preamble to the proposed rule, there are a
number of methods which can measure dpm concentrations with reasonable
accuracy when it is at high concentrations and when the purpose is
exposure assessment. Measurements for the purpose of compliance
determinations must be more accurate, especially if they are to measure
compliance with a dpm concentration as low as 200 g/m\3\ or
lower. Accordingly, MSHA noted that it needed to address a number of
questions as to whether any existing method could produce accurate,
reliable and reproducible results in the full variety of underground
mines, and whether the samplers and laboratories existed to support
such determinations. (See 63 FR 58127 et.seq).
MSHA concluded that there was no method suitable for such
compliance measurements in underground coal mines, due to the inability
of the available methods to distinguish between dpm and coal dust.
Accordingly, the agency developed a rule for the coal mining sector
that does not depend upon ambient dpm measurements.
By contrast, the agency concluded that by using a sampler developed
by the former Bureau of Mines, and an analytical method developed by
the National Institute for Occupational Safety and Health (NIOSH), MSHA
could accurately measure dpm levels at the required concentrations in
underground metal and nonmetal mines. While not requiring operators to
use this method for their own sampling, MSHA did commit itself to use
this approach (or a method subsequently determined by NIOSH to provide
equal or improved accuracy) for its own sampling. Moreover the agency
proposed that MSHA sampling be the sole basis for determining
compliance by metal and nonmetal mine operators with applicable
compliance limits, and that a single sample would be adequate for such
purposes. Specifically, proposed Sec. 57.5061 would have provided:
Section 57.5061 Compliance determinations.
(a) A single sample collected and analyzed by the Secretary in
accordance
[[Page 5719]]
with the procedure set forth in paragraph (b) of this section shall be
an adequate basis for a determination of noncompliance with an
applicable limit on the concentration of diesel particulate matter
pursuant to Sec. 57.5060.
(b) The Secretary will collect and analyze samples of diesel
particulate matter by using the method described in NIOSH Analytical
Method 5040 and determining the amount of total carbon, or by using any
method subsequently determined by NIOSH to provide equal or improved
accuracy in mines subject to this part.
This part of MSHA's proposed rule received considerable comment.
Some commenters challenged the accuracy, precision and sensitivity of
NIOSH Analytical Method 5040. Some challenged whether the amount of
total carbon determined by the method is a reliable way to determine
the amount of dpm. Others questioned whether the sampler developed by
the former Bureau of Mines would provide an accurate sample to be
analyzed. Many commenters asserted that the analytical method would not
be able to distinguish between dpm and various other substances in the
atmosphere of underground metal and nonmetal mines--carbonates and
carbonaceous minerals, graphitic materials, oil mists and organic
vapors, and cigarette smoke. (It should be noted that commenters also
questioned the use of a single sample as the basis for a compliance
determination, and the use of area sampling in compliance
determinations; these comments are reviewed and responded to in Part IV
of this preamble in connection with the discussion of Sec. 57.5061.)
The agency has carefully reviewed the information and data
submitted by commenters. Where necessary to verify the validity of
comments, MSHA collected additional information which it has placed in
the record, and which in turn were the subject of an additional round
of comments.
Background. As discussed in section 2 of this part, diesel
particulate consists of a core of elemental carbon (EC), adsorbed
organic carbon (OC) compounds, sulfates, vapor phase hydrocarbons and
traces of other compounds. The method developed by NIOSH provides for
the collection of a sample on a quartz fiber filter. As originally
conceived, the filter is mounted in an open face filter holder that
allows for the sample to be uniformly deposited on the filter surface.
After sampling, a section of the filter is analyzed using a thermal-
optical technique (Birch and Cary, 1996). This technique allows the EC
and OC species to be separately identified and quantified. Adding the
EC and OC species together provides a measure of the total carbon
concentration in the environment.
Studies have shown that the sum of the carbon (C) components (EC +
OC) associated with dpm accounts for 80-85% of the total dpm
concentration when low sulfur fuel is used (Birch and Cary, 1996).
Therefore, in the preamble to the proposed rule, MSHA asserted that
since the TC:DPM relationship is consistent, it provides a method for
determining the amount of dpm. MSHA noted that the method can detect as
little as 1 g/m3 of TC. Moreover, NIOSH has
investigated the method and found it to meet NIOSH's accuracy criterion
(NIOSH, 1995)--i.e., that measurements come within 25 percent of the
true TC concentration at least 95 percent of the time.
In the preamble to the proposed rule, MSHA recognized that there
might be some interferences from other common organic carbon sources in
underground metal and nonmetal mines: specifically, oil mists and
cigarette smoke. The agency noted it had no data on oil mists, but had
not encountered the problem in its own sampling. With respect to
cigarette smoke, the agency noted that: ``Cigarette smoke is under the
control of operators, during sampling times in particular, and hence
should not be a consideration.'' (63 FR 58129).
The agency also discussed the potential advantages and
disadvantages of using a special device on the sampler to eliminate
certain other possible interferences. NIOSH had recommended the use of
a submicron impactor when taking samples in coal mines to filter out
particles more than one micron in size. See Figure III-3. The idea is
to ensure that a sample taken in a coal mine does not include
significant amounts of coal dust, since the analytical method would
capture the organic carbon in the coal dust just like the carbon in
dpm. Coal dust is generally larger than one micron, while dpm is
generally smaller than one micron. However, MSHA pointed out that while
samples in underground metal and nonmetal mines could be taken with a
submicrometer impactor, this could lead to underestimating the total
amount of dpm present. This is because the fraction of dpm particles
greater than 1 micron in size in the environment of noncoal mines can
be as great as 20%.
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MSHA also noted that while NIOSH Method 5040 requires no
specialized equipment for collecting a dpm sample, the sample would
most probably require analysis by a commercial laboratory. The agency
noted it did not foresee the availability of qualified testing
facilities as a problem. The agency likewise discussed the availability
of the sampling device, and noted steps that were underway to develop a
disposable sampler. (63 FR 58130)
Sample Collection Methods. Some commenters raised questions about
how dpm samples should be taken: using open face sampling, respirable
sampling and submicron sampling. All three are discussed in NIOSH
Analytical Method 5040. Because diesel particulate matter is primarily
submicron in size any of the three sampling methods could be used.
The choice of sample collection method considers the cost and
potential interferences that the method can contribute. Regardless of
the sampling method, the sampling media (filter) must be one that does
not interfere with the analysis. For this reason a pre-fired quartz
fiber filter has been chosen. The quartz fiber filter is capable of
withstanding the temperatures from the analytical procedure. The filter
is pre-fired to remove residual carbon, attached to the filter during
manufacturing.
Total Dust Sampling. Total dust sampling is the least expensive
method to collect an airborne dust sample. It is commonly used to
collect a sample that is representative of all the dust in the
environment; i.e., the particles are not preclassified during the
collection process. Total dust sampling can be performed using a filter
cassette that allows the whole face of the filter to be exposed during
collection of the sample (open face) or using a filter cassette with a
small inlet opening (referred to as a closed face filter cassette). The
latter method is used by MSHA for compliance sampling for total dust in
the metal and nonmetal sector. Because the sample collected is
representative of all the particulate matter in the environment, there
is the potential for interference from mineral contaminants when
sampling for diesel particulate matter. While in many cases the
analytical results can be corrected for these interferences, in some
instances the interferences may be so large that they can not be
quantified with the analytical procedure, thus preventing the
analytical result to be corrected for the interference.
Additionally, MSHA has noted that in some cases when using the
total dust sampler with the small inlet hole, distribution of the
collected sample on the filter is not uniform. The distribution of
sample is concentrated in the center of the filter. This can result in
the effect of an interference being magnified. As a result, MSHA
considers that total dust sampling is not an appropriate sampling
method for the mining industry to use when sampling diesel particulate
matter.
Respirable Dust Sample Collection. Respirable dust sampling is
commonly used when a size selective criteria for dust is required. The
mining industry is familiar with size selective sampling for the
collection of coal mine dust samples in coal mines and for collecting
respirable silica samples in metal and nonmetal mines. For respirable
dust sampling MSHA uses a 10 millimeter, Dorr Oliver nylon cyclone as a
particle classifier to separate the respirable fraction of the aerosol
from the total aerosol sampled. The use of this particle classifier
would be suitable when sampling diesel particulate, provided
significant amounts of interfering minerals are not present. This is
because 90 percent of the diesel particulate is typically less than 1
micrometer in size. Particles less than 1 micrometer in size pass
through the cyclone and are deposited on the filter. While in many
cases, these interferences could be removed during the analytical
procedures, the analytical procedures alone can not be assured to
remove the interferences when large amounts of mineral dust are
present.
Additionally, MSHA has observed that in some sampling equipment the
cyclone outlet hole has been reduced when interfacing it with the
filter capsule. MSHA has further observed that where this has occurred,
the distribution of sample on the collection filter may not be uniform.
In this circumstance the sample is also concentrated in the center of
the filter which can result in the effect of a mineral interference
being magnified. As a result, MSHA considers that respirable dust
sampling is not a universally applicable sampling method for the mining
industry to use for sampling diesel particulate matter.
Submicron Dust Sample Collection. Since only a small fraction of a
mineral dust aerosol is less than 1 micrometer in size, a submicrometer
impactor (Cantrell and Rubow, 1992) was developed to permit the
sampling of diesel particulate without sampling potential mineral
interferences. The submicrometer impactor was initially developed to
remove the interference from coal mine dust when sampling diesel
particulate in coal mines. It was designed to remove the carbon coal
particles, that are greater than 0.8 micrometer in size, when sampling
for diesel particulate matter at a pump flowrate of 2.0 liters per
minute. As a result the submicrometer impactor cleans potentially
interfering mineral dust from the sample.
As noted in the preamble to the proposed rule, use of this method
to measure dpm does result in the exclusion of that portion of dpm that
is not submicron in size, and this can be significant. On the other
hand, this method avoids problems associated with the other methods
described above. Moreover, as discussed in more detail below under the
topic of ``interferences'', the submicron impactor can eliminate
certain substances that in metal and nonmetal mines would otherwise
make it difficult for the analytical method to be used for compliance
purposes.
Accuracy of Analytical Method, NIOSH Method 5040. Commenters
challenged the accuracy, precision and sensitivity of the analytical
method (NIOSH Method 5040) used for the diesel particulate analysis.
MSHA has carefully reviewed these concerns, and has concluded that
provided a submicron impactor is used with the sampling device in
underground metal and nonmetal mines, NIOSH Method 5040 does provide
the accuracy, precision and sensitivity necessary to use in compliance
sampling for dpm in such mines.
As noted above, NIOSH Method 5040 is an analytical method that is
used to determine elemental and organic carbon content from an airborne
sample. It is more versatile than other carbon analytical methods in
that it differentiates the carbon into its organic and elemental carbon
components. The method accomplishes this through a thermal optical
process. An airborne sample is collected on a quartz fiber filter. A
portion of the filter, (approximately 2 square centimeters in area) is
placed into an oven. The temperature of the oven is increased in
increments. At certain oven temperature and atmospheric conditions
(helium, helium-oxygen), carbon on the filter is oxidized into carbon
dioxide. The carbon dioxide gas is then passed over a catalyst and
reduced to methane. The methane concentration is measured and carbon
content is determined. Separation of different types of organic carbon
is accomplished through temperature and atmospheric control. The
instrument is programmed to increase temperature in steps over time.
This step by step increase in temperature allows for differentiation
between various types of organic carbon.
[[Page 5722]]
A laser is used to differentiate the organic carbon from the
elemental carbon. The laser penetrates the filter and when the laser
transmittance reaches its initial value this determines when elemental
carbon begins to evolve. The computer software supplied with the
instrumentation indicates this separation by a vertical line. The
separation point can be adjusted by the analyst. As a result, there may
be small differences in the determination of organic and elemental
carbon between analysts, but the total carbon (sum of elemental and
organic carbon) does not change. The software also allows the analyst
to identify and quantify the different types of organic carbon using
identifiable individual peaks. This permits the mathematical
subtraction of a particular carbon peak. This feature is particularly
useful in removing contributions from carbonates or other carbonaceous
minerals. In other total carbon methods, samples have to be acidified
to remove carbonate interference. A thermogram is produced with each
analysis that shows the temperature ramps, oven atmospheric conditions
and the amount of carbon evolved during each step.
A range of five separate sucrose standards between 10-100
g/cm\2\ carbon are initially analyzed to check the linearity
of the internal calibration determined using a constant methane
concentration. This constant methane concentration is injected at the
end of each analysis. To monitor this methane constant, sucrose
standards are analyzed several times during a run to determine that
this constant does not deviate by more than 5-10%.
The method has the sensitivity to analyze environmental samples
containing 1 to 10 g/m\3\ of elemental carbon. The method will
be used in mining applications to determination total carbon
contamination where the diesel particulate concentration will be
limited to 400 g/m\3\TC and 160 g/
m\3\TC. NIOSH has reported that the lower limit of detection
for the method is 0.1 g/cm\2\ elemental carbon for an oven
pre-fired filter portion and 0.5 g/cm\2\ organic carbon for an
oven pre-fired filter portion. For a full shift sample, this detection
limit represents approximately 1 and 5 g/m\3\ of elemental and
organic carbon, respectively. Additionally, NIOSH has conducted a round
robin program to assess interlaboratory variability of the method. This
study indicated a relative standard deviation for total carbon, of less
than 15 percent.
A typical diesel particulate thermogram is shown in Figure II-4.
The thermogram generally contains five or six carbon peaks, one for
each temperature ramp on the analyzer. The first four peaks (occurring
during a helium atmosphere ranging from a temperature of 210C to 870C)
are associated with organic carbon determination and the fifth and/or
sixth peak (occurring during a helium/oxygen atmosphere ranging in
temperature from 610C to 890C) is the elemental carbon determination.
The fourth peak (temperature ~750C) is also where carbonate and
other carbonaceous minerals are evolved in the analysis. For a diesel
particulate sample without interferences present, this fourth peak is
usually minimal as it is attributed to heavy distillant organics not
normally associated with diesel operations in underground mining
applications. If this peak is due to carbonate, the carbonate
interference can be verified by analyzing a second portion of the
sample after acidification as described in the NIOSH 5040 method. If
the fourth peak is caused by some other carbonaceous mineral, the
acidification process may not completely remove the interference and
may, on occasion cause a positive bias to elemental carbon.
As explained below in the discussion of interferences, these
analytical interferences from carbonaceous materials can be corrected
by using the submicron impactor preceded by a cyclone (respirable
classifier) to collect diesel particulate matter samples, since nearly
all the particles of these minerals are greater than 1 micrometer in
size. Accordingly, MSHA has determined it should utilize a submicron
impactor in taking any samples in underground metal and nonmetal mines,
and has included this requirement in the rule. Specifically, 57.5061(b)
now provides:
(b) The Secretary will collect samples of diesel particulate matter
by using a respirable dust sampler equipped with a submicrometer
impactor and analyze the samples for the amount of total carbon using
the method described in NIOSH Analytical Method 5040, except that the
Secretary may also use any methods of collection and analysis
subsequently determined by NIOSH to provide equal or improved accuracy
for the measurement of diesel particulate matter in mines subject to
this part.
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[[Page 5724]]
In keeping with established metal and nonmetal sampling protocol,
the samplers will be operated at a flow rate of 1.7 LPM. At a flow rate
of 1.7 LPM, the cut point for the impactor is 0.9 micrometers.
Any organic carbon detected at the fourth peak will be subtracted
from the organic carbon portion of the sample analysis using the
software supplied with the analytical program. The only samples that
MSHA anticipates that will be acidified are those collected in trona
mines. These samples contain a bicarbonate which evolves in several of
the organic peaks but can be removed by acidification. Use of the
submicron impactor will also insure a uniform distribution of diesel
particulate and mineral dust on the filter.
Some Commenters indicated that a uniform deposit of mineral dust
was sometimes not obtained with certain respirable dust sampler
configurations. For some commodities such as salt and potash, where
carbonate may not be an interference, it is probably not necessary to
sample with the submicron impactor. However, in order to be consistent,
MSHA will sample all commodities using a respirable dust sampler
equipped with a submicrom impactor, and has so noted in the rule.
Proper use of sample blanks. Each set of samples collected to
measure the diesel particulate concentration of a mine environment,
must be accompanied by a field blank (a filter cassette that is treated
and handled in the same manner as filters used to collect the samples)
when submitted for analysis. The amount of total carbon determined from
the analysis of the blank sample must be applied to (subtracted from)
the carbon analysis of each individual sample. The field blank
correction is applied to account for non-sampled carbon that attaches
to the filter media. The blank correction is applied to the organic
fraction as, typically, no elemental carbon is found on the blank
filters.
Failure to adjust for the blanks can lead to incorrect results, as
was the case with samples collected by some commenters. While field
blanks were submitted and analyzed with their samples, the field blank
analytical results were not used to correct the individual samples for
nonsampled carbon content. Typically the carbon content on the reviewed
field blanks ranged from 2 to 3 g/square centimeter of filter
area. For a one-hour sample, not using a blank correction of this
magnitude, could result in an overestimate of 250 g/m\3\ of
dpm (3 x 8.55 x 1000/(1.7 * 60)=250). For an eight-hour sample, not
using a blank correction, could result in an overestimate of 30
g/m\3\ of dpm (3 x 8.55 x 1000/(1.7* 480)=30).
Variability of Sample Blanks
In response to the July 1, 2000, reopening of the record, one
commenter submitted summary data from a study that examined diesel
exposures in seven underground facilities where trona, salt, limestone,
and potash were mined. The purpose of this study was to determine the
precision and accuracy of the NIOSH 5040 method in these environments.
According to the commenter, the study data ``provide strong evidence
that the NIOSH 5040 Method * * * is not feasible as a measure of DPM
exposure.'' The commenter's conclusion was based on five
``difficulties'' that, according to the commenter, were documented when
sampling for DPM using organic carbon or total carbon as a surrogate.
These difficulties were:
(1) High and variable blank values from filters;
(2) High variability from duplicate punches from the same sampling
filter;
(3) Consistently positive interference when open-faced monitors
were sampled side-by-side with cyclones;
(4) Poor correlation of organic carbon to total carbon levels; and
(5) Interference from limestone that could not be adequately
corrected with acid-washing.
As discussed elsewhere in this preamble, difficulties #3 and #5
will be resolved by the use of a submicrometer impactor sampler.
Difficulty #4, the lack of a strong correlation between organic carbon
and total carbon, has long been recognized by MSHA. That is one of the
reasons MSHA chose total carbon (TC=EC+OC) as the best surrogate to use
for assessing DPM levels in underground metal and nonmetal mines. MSHA
has never proposed using organic carbon as a surrogate measure of DPM.
The summary data that the commenter submitted do not appear to
demonstrate the first two items of ``difficulties'' with respect to TC
measurements. Because MSHA has not experienced the difficulties of (1)
high and variable blank values and (2) high variability between
duplicate punches from the same sampling filter, MSHA also performed
its own analysis of the data submitted by the commenter. MSHA's
examination of the data included:
Estimating the mean, within-mine standard deviation, and
relative standard deviation (RSD) for blank TC values, based on the
``Summary of Blank Sample Results'' submitted; and
Estimating the variability (expressed as RSD) associated
with the TC analysis of duplicate punches from the same filter, based
on individual sample data submitted earlier by the same commenter for
five of the mines.
Based on the summary data, the overall average mean TC content per
blank filter, weighted by the number of blank samples in each mine, was
16.9 g TC. This represents the average value that would be
subtracted from the TC measurement from an exposed sample before making
a noncompliance determination. At a TC concentration of 160 g/
m3 (the final limit established by this rule), the TC
accumulated on a filter after an 8-hour sampling period would be
approximately 130 g. Therefore, these data show that the mean
TC value for a blank is less than 13 percent of TC accumulated at the
concentration limit, and an even lower percentage of total TC
accumulated at concentrations exceeding the limit. MSHA considers this
to be acceptable for samples used to make noncompliance determinations.
Based on the same summary data presented for TC measurements on blank
samples, the weighted average of within-mine standard deviations is 6.4
g. Compared to TC values greater than or equal to 130
g, this corresponds to an RSD no greater than 6.4/130 = 4.9
percent. MSHA also regards this degree of variability in blank TC
values to be acceptable for purposes of noncompliance determination.
To estimate the measurement variability associated with analytical
errors in the TC measurements, MSHA examined the individual TC results
from duplicate punches on the same filter. These data were submitted
earlier by the same commenter for five mines. As shown, by the
commenter's summary table, data obtained from the first mine were
invalid, leaving data from four mines (2-5) for MSHA's data analysis.
Data were provided on a total of 73 filters obtained from these four
mines, yielding 73 pairs of duplicate TC measurements, using the
initial and first repeated measurement provided for both elemental and
organic carbon. MSHA calculated the mean percent difference within
these 73 pairs of TC measurements (relative to the average for each
pair) to be 8.2 percent (95-percent confidence interval = 5.6 to 10.9
percent). Based on the same data, MSHA calculated an estimated RSD =
10.0 percent for the analytical error in a single determination of
TC.\1\ Contrary
[[Page 5725]]
to the commenter's conclusion, this result supports MSHA's position
that TC measurements do not normally exhibit excessive analytical
errors.
---------------------------------------------------------------------------
\1\ This estimate was obtained by first calculating the standard
deviation of the differences between the natural logarithms of the
TC measurements within each pair. Since each of these differences
contains two TC determinations, and two corresponding analytical
errors, this standard deviation was divided by the square root of 2.
Using standard propagation of error formulas, the result provides a
reasonably good estimate of the RSD over the range of TC values
reported. MSHA used the same technique to estimate the RSD for the
25 pairs of TC samples analyzed at different laboratories, as
described below.
---------------------------------------------------------------------------
This estimate of the RSD = 10.0 percent for TC measurements is also
consistent with the replicated area sample results submitted by the
commenter for the seven mines. In this part of the study, designed to
evaluate measurement precision, 69 sets of simultaneous samples were
collected at the seven mines. Each set, or ``basket,'' of samples
normally consisted of five simultaneous samples taken at essentially
the same location. Since the standard deviation of the TC measurements
within each basket was based on a maximum of five samples, the standard
deviation calculated within baskets is statistically unstable and does
not provide a statistically reliable basis for estimating the RSD
within individual baskets. However, as shown in the summary table
submitted by the commenter, the mean RSD across all 69 baskets was 10.6
percent. This RSD, which includes the effects of normal analytical
variability, variability in the volume of air pumped, and variability
in the physical characteristics of individual sampler units, is not
unusually high, in the context of standard industrial hygiene practice.
MSHA also examined data submitted by another commenter to estimate
the total variability associated with TC sample analysis by different
laboratories. Based on 25 pairs of simultaneous TC samples (using a
cyclone) analyzed by different laboratories, this analysis showed a
total RSD of approximately 20.6 percent. If the most extreme of three
statistical outliers in these data is excluded, the result based on 24
pairs is an estimated RSD of 11.7 percent. Like the first commenter's
estimate of RSD = 10.6 percent, based on simultaneous samples analyzed
at the same laboratory, these RSD's include not only normal analytical
variability in a TC determination, but also variability in the volume
of air pumped and variability in the physical characteristics of
individual sampler units. The higher estimates, however, also cover
uncertainty in a TC measurement attributable to differences between
laboratories.
Based on these analyses, MSHA has concluded that the data submitted
to the record by commenters support the Agency's position that NIOSH
Method 5040 is a feasible method for measuring DPM concentrations in
underground M/NM mines.
Availability of analysis and samplers. One of the concerns
expressed by commenters was the limited number of commercial
laboratories available to analyze diesel particulate samples, and the
availability of required samplers. While MSHA will be doing all
compliance sampling itself, and running the analyses in its AIHA
accredited laboratory in Pittsburgh, pursuant to Sec. 57.5071 of the
rule, operators in underground metal and nonmetal mines will be
required to do environmental monitoring; and although they will not be
required to use the same methods as MSHA to determine dpm
concentrations, MSHA presumes that many will wish to do so. Moreover,
there are certain situations (e.g., verification that a dpm control
plan is working) where the rule requires operators to use this method
(Sec. 57.5062(c)).
Currently there are four commercial labs that have the capability
to analyze for dpm using the NIOSH 5040 Method. These labs are: Sunset
Laboratory, Forest Grove, Oregon and Chapel Hill, North Carolina; Data
Chem, Salt Lake City, Utah; and Clayton Group Services, Detroit, MI.
All of these labs, as well as including the NIOSH Laboratories in
Cincinnati and Pittsburgh and the MSHA laboratory in Pittsburgh
participate in a round robin analytical test to verify the accuracy and
precision of the analytical method being used by each. As MSHA
indicated in the preamble to its proposed rule, it believes that once
there is a commercial demand for these tests, additional laboratories
will offer such services.
The cost of the analysis from the commercial labs is approximately
$30 to $50 for a single punch analysis and a report. This is about the
same amount as a respirable silica analysis. The labs charge another
$75 to acidify and analyze a second punch from the same filter and to
prepare an analytical report. The labs report both organic and
elemental carbon. By using the submicron impactor, operators can
significantly reduce the number of situations where acidification is
required, and thus reduce the cost of sample analysis.
The availability of samplers has been the subject of many
comments--not so much because of concern about availability once the
rule is in effect, but because of assertions that they are not
available now. In particular, it has been alleged by some commenters
that they have been unable to conduct their own ``independent
evaluation'' of the NIOSH method because the agency has kept from them
the samplers needed to properly conduct such testing. Some commenters
even accused the agency of deliberately withholding the needed
samplers.
As indicated in MSHA's toolbox and the preamble to the proposed
rule, the former Bureau of Mines (BOM) submitted information on the
development of a prototype dichotomous impactor sampling device that
separates and collects the submicron respirable particulate from the
respirable dust sampled. Information on this sampling device has been
available to the industry since 1992. A picture of the sampler is shown
above as Figure II-3. The impactor plate is made out of brass and the
nozzles are drilled. The former BOM made available to all interested
parties detailed design drawings that permitted construction of the
dichotomous impactor sampler by any local machine shop. NIOSH and MSHA
had hundreds of these sampling devices made for use in their programs
to measure dpm concentrations. Anyone could have had impactor samplers
built by a local machine shop at a cost ranging from $50 to $100.
In 1998, MSHA provided NIOSH with research funds for the
development of a disposable sampling device that would have the same
sampling characteristics as the BOM sampler, and including an impactor
with the same sampling characteristics as the metal one. NIOSH awarded
SKC the contract for the development of the disposable sampler. MSHA
estimates the cost of the disposable sampler will be less than $50. The
sampler is designed to interface with the standard 10 millimeter Dorr
Oliver cyclone particle classifier and to fit in a standard MSHA
respirable dust breast plate assembly. The quartz fiber filter used for
the collection of diesel particulate in accordance with NIOSH Method
5040 has been encapsulated in an aluminum foil to make handling during
the analytical procedure easier. To reduce manufacturing expense (and
therefore, sampler cost), the nozzle plate in the SKC sampler is made
of plastic instead of brass. In order to ensure that the nozzles in the
impaction plate would hold their tolerances during manufacturing, the
plastic nozzle plate for the SKC sampler is fitted with synthetic
sapphire nozzles. This nozzle plate and nozzle assembly have the same
performance as the BOM-designed sampler.
[[Page 5726]]
As of the time MSHA conducted its verification sampling for
interferences, SKC had developed several prototypes of the disposable
unit. However, testing of the devices by NIOSH indicated that a minor
design modification was needed to better secure the impaction plate and
nozzle plate to the sampler housing for a production unit. In its
verification sampling, MSHA used both BOM designed and SKC prototype
samplers. Prior to its verification tests, MSHA replaced the brass
nozzle plates in the BOM design impactors with plastic nozzle-plates
fitted with sapphire nozzles, as used in the SKC prototype sampler.
However, because there was no change in nozzle geometry, this change in
the BOM impactors did not affect their performance. During MSHA's
verifications testing, no problems were experienced with dislodgement
of the impaction plates or nozzle plates. The impactors used by MSHA in
its verification sampling were not defective in any way, as suggested
by several Commenters.
Under the Mine Act, MSHA has no obligation to make devices
available to the mining community to conduct its own test sampling or
to verify MSHA's results, nor does the mining industry have any
explicit authority under the Mine Act to ``independently evaluate''
MSHA's results. The responsibility for determining the accuracy of the
device and method for sampling rests with the agency, not the mining
community. Accordingly, although some commenters requested that MSHA
remove its interference studies from the record, the agency declines to
do so. These studies are discussed in more detail below; additional
questions raised about the sampling devices used in the studies, and
the procedures for that sampling, are discussed in that context.
Some commenters initially asserted that their inability to conduct
their own testing would prevent them from making comments of MSHA's
verification studies. Based on the detailed comments subsequently
provided, this initial concern appears to have been overstated.
It appears from some of the comments on MSHA's studies that members
of the mining community may have understood MSHA to say that use of an
impactor sampler would remove all interferences. MSHA can find no such
statement. As noted in more detail below, use of the impactor will
remove most of the interferences (albeit at the cost of eliminating
some dpm as well).
Choice of Total Carbon as Measurement of Diesel Particulate Matter.
MSHA asserted that the amount of total carbon (determined by the
sampling and analytical methods discussed above) would provided the
agency with an accurate representation of the amount of dpm present in
an underground metal and nonmetal mine atmosphere at the concentration
levels which will have to be maintained under the new standard. Some
commenters questioned MSHA's statements concerning the consistency of
the ratio between total carbon and diesel particulate, and the amount
of that ratio. Other commenters suggested that elemental carbon may be
a better indicator of diesel particulate because it is not subject to
the interference that could effect a total carbon measurement.
Under the approach incorporated into the final rule, the
concentration of organic and elemental carbon (in g per square
centimeter) are separately determined from the sample analysis and
added together to determine the amount of total carbon. The
interference from carbonate or mineral dust quantified by the fourth
organic carbon peak is subtracted from the organic carbon results. The
field blank correction is then subtracted from the organic analysis
(the blank does not typically contain elemental carbon). Concentrations
(time weighted average) of carbon are calculated from the following
formula:
[GRAPHIC] [TIFF OMITTED] TR19JA01.099
Where:
C=The Organic Carbon (OC) or Elemental Carbon (EC) concentration,
in g/m\3\, measured in the thermal/optical carbon analyzer
(corrected for carbonate and field blank).
A=The surface area of the filter media used. The surface areas of
the filters are as follows: quartz fiber filter without aluminum cover
is 8.55 cm\2\; quartz fiber filter with aluminum cover is 8.04 cm\2\.
The 80 percent factor MSHA used to establish the total carbon level
equivalents of the 500 g/m\3\ and 200 g/m\3\ dpm
concentration limits being set by the rule was based on information
obtained from laboratory measurements conducted on diesel engines
(Birch and Cary, 1996). Since the publishing of the proposed rule, this
value has been confirmed by measurements collected in underground mines
in Canada (Watts, 1999)
MSHA agrees that the total carbon measurement is more subject to
interferences than the elemental carbon measurement. However, because
the ratio of elemental carbon to total carbon in underground mines is
dependent on the duty cycle at which the diesel engine is operated
(found to vary between 0.2 and 0.7), MSHA believes that total carbon is
the best indicator of diesel particulate for underground mines.
Additionally, MSHA has observed that some controls, such as filtration
systems on cabs can alter the ratio of elemental to total carbon. The
ratio can be different inside and outside a cab on a piece of diesel
equipment. MSHA notes that NIOSH has asserted that the ratio of
elemental carbon to dpm is consistent enough to provide the basis for a
standard based on elemental carbon (``* * * the literature and the MSHA
laboratory tests support the assertion that DPM, on average, is
approximately 60 to 80% elemental carbon, firmly establishing EC as a
valid surrogate for DPM''). However, while an average value for
elemental carbon percent may be a useful measure for research purposes,
data submitted by commenters show that elemental carbon can range from
8 percent to 81 percent of total carbon.
MSHA does not believe elemental carbon is a valid surrogate for dpm
in the context of a compliance determination that, like all other metal
and nonmetal health standards, can be based on a single sample. By
contrast, as noted above, studies have shown that there is a consistent
ratio between total carbon and dpm (from 80 to 85%). Moreover, although
the ratio of the elemental carbon to organic carbon components obtained
using the NIOSH Method 5040 may vary, total carbon determinations
obtained with this method are very consistent, and agree with other
carbon methods (Birch, 1999). Accordingly, while total carbon sampling
does necessitate sampling protocols to avoid interferences, of the sort
discussed below, MSHA has concluded that it would not be suitable at
this time to use elemental carbon as a surrogate for dpm.
Potential Sample Interferences/Contributions. As noted in the
introduction to this section, many commenters asserted that the
analytical method would not be able to distinguish between dpm and
various other substances in the atmosphere of underground metal and
nonmetal mines--carbonates and carbonaceous minerals, graphitic
materials, oil mists and organic vapors, and cigarette smoke. The
agency carefully reviewed the information submitted by commenters, both
during the hearings and in writing, and found that it was in general
insufficient to establish that such interferences would be a problem.
Limitations in the data submitted by the
[[Page 5727]]
commenters included, for example, failure to utilize blanks, failure to
blank correct sample results, open face and respirable samples that
were collected in the presence of high levels of carbonate
interference, the amount of carbonate interference was not quantified,
dpm was not uniformly deposited on filters and sample punches were
taken where the deposit was heaviest, failure to adjust sample results
due to short sampling times, failure to consider the impact of
interferences such as carbonate, oil mist, and cigarette smoke on dpm
exposure.
Rather than dismiss these assertions, however, the agency decided
to conduct some investigations to verify the validity of the comments.
As a result of these tests, the agency has determined that certain
interferences can exist, within certain parameters; and was also able
to demonstrate how these interferences can be minimized or avoided. The
material which follows reviews the information MSHA has on this topic,
including representative comments MSHA received on these verification
studies. Part IV of this preamble reviews in some detail the
adjustments MSHA has made to the proposed rule, and the practices MSHA
will follow in compliance sampling, to avoid these interferences.
General discussion of interference studies. As noted above, MSHA
conducted the verifications to determine if the alleged interferences
were in fact measurable in underground mining environments. At the same
time, the studies gave MSHA an opportunity to identify sampling
techniques that would minimize or eliminate the interferences, evaluate
analytical techniques to minimize or eliminate the interferences from
the samples, and develop a sampling and analytical strategy to assure
reliable dpm measurements in underground mines.
A total of six studies were conducted. One field study was
conducted at Homestake Mine, a gold mine in Lead, South Dakota, three
field studies were conducted at gold mines near Carlin, Nevada. These
included Newmont, South Area Carlin Mine and Barrick Goldstrike. One
study was conducted in the NIOSH Research Laboratory's experimental
mine in Pittsburgh, Pennsylvania and one study conducted in a
laboratory dust chamber at the NIOSH Pittsburgh Research Laboratory.
For example the studies conducted at Carlin and Homestake were to
evaluate interference from oil mist and the studies conducted at
Homestake, Newmont and Barrick were to assess interference from
carbonaceous dust. These locations were carefully selected in light of
the assertions about interferences which had been made by commenters.
Despite the care that went into designing where to conduct the
verification samples, there were a number of comments asserting the
samples were not representative. For example, it was asserted that MSHA
did not sample a representative particle size distribution and sampled
the wrong material (i.e., ores with the highest carbon content). On the
contrary the samples that MSHA collected were representative of the
respirable and submicron fractions of the dust in the environment as
well as the total dust in the environment. Therefore, MSHA believes
that the particle size distribution of the samples collected were
representative. Also, MSHA obtained a bulk sample of the various ores
tested. While the samples collected at the crushers were low carbon
content (0-10.3%), the carbon content (30.3%) of the ore collected at
the underground mining area sampled at Carlin was similar to the high
carbon content (31.4%) ores obtained at Barrick. The sampling therefore
included a cross section of the ores in question.
Some commenters objected to the fact that no personal samples were
collected in these studies. Packages of samplers were placed in areas
that were close to the breathing zone of the workers. Upwind and
downwind samples were used to determine the extent of the interference.
The regulation recognizes the validity of area samples. As a result
these samples provided valid information on interferences that are
likely to be encountered during sampling by MSHA inspectors.
More generally, commenters asserted that MSHA lacked enough studies
for statistical analysis. MSHA notes again that the studies were
conducted to verify specific industry assertions, and were properly
designed to try and verify those assertions. However, the same studies
which confirmed that such interferences could be measured in certain
conditions were also able to determine that these interferences could
not be measured, or were not significant in scope, if some of the
conditions were changed. Part IV of this preamble discusses what
actions the agency plans to take as a result of its current information
on this matter.
Some commenters asserted that MSHA made certain incorrect technical
assumptions in its verification sampling: about the sampling method
used to conclude that overall dust levels would meet MSHA's standards;
about the concentration of EC in submicrometer dust; and about the
variability of carbonaceous ores. With respect to the first point, the
final sampling strategy adopted by MSHA for dpm allows for either
personal or area sampling using a submicrometer sampler preceded by a
respirable cyclone. Because of the sampling and analytic procedures,
the only potential mineral interferent would be the graphitic
contribution (elemental carbon). The carbonate and carbonaceous
contribution would be eliminated or reduced by the use of the impactor
sampler and using the software integration procedure described in
Method 5040.
With respect to the second point, the concentration of EC in the
submicrometer dust, for personal and most area samples, the allowable
silica exposure would limit the amount of submicrometer mineral dust
sampled. This has been demonstrated for samples collected in coal mines
where the coal dust contains high levels of elemental carbon, but the
interference for EC from submicrometer samples has been less that 4
g/m3.
With respect to the last point which addresses the geology of the
ore, MSHA acknowledges that there would be variation in the carbon
content of the ore. However, it would be unlikely that the carbon
content would exceed that of coal mine dust where the elemental carbon
interference has been found to be negligible.
The sampling was performed with the BOM designed or SKC prototype
samplers as described in the prior section. All samplers used the more
precise sapphire nozzles. Samples were collected using standard
procedures developed by MSHA for assessing particulate concentrations
in mine environments. Samples were analyzed for total carbon using
NIOSH Method 5040. The analyses was performed by MSHA at the Pittsburgh
Safety and Health Technology Center's Dust Division laboratory. For
some samples a second analysis was performed using an acidification
procedure.
Commenters alleged a number of technical problems with how the
sampling was performed. Some asserted that defective devices were used
for the sampling, or that MSHA did not properly calibrate its
equipment. MSHA did not experience any problems with the samplers, and
did calibrate its equipment according to standard procedures. Some
pointed out that MSHA conducted the verifications with samplers
different from those required by the rule. MSHA presumes this comment
reflects the fact that the proposed rule did not require an
[[Page 5728]]
impactor to be used; this is, however, the case with the final rule.
Some commenters noted that MSHA voided some sample results and
that, lacking further explanation, it might be assumed the agency
simply eliminated those samples which gave results that did not agree
with the conclusions it sought. The only samples that were voided were
chamber samples. Some voided samples were higher than, and some void
samples were lower than, the sample used. These were duplicate samples
collected for short time periods. Samples were voided because they were
inconsistent with other samples in the set of six samples collected.
These inconsistencies as-well-as variability between other duplicate
samples were attributed to short sample times. Voided sample results
are shown for Homestake (1 of 12 impactors). No impactor samples were
voided at Barrick nor at the Newmont crusher. In the Jackleg drill
tests conducted at Carlin Mine, there were 2 of 6 impactor samples
voided.
Others asserted that MSHA failed to validate the design of the box
which held the sampling equipment. In fact, all of the issues mentioned
relative to the sampling box (i.e., pressure build up, leakage of
chamber, impaction of particles, pump calibration) had been carefully
examined by MSHA prior to the tests and found not to be a problem.
Also, this sample chamber has been used extensively in other field
tests where duplicate samples or a variety of samplers have been used
and has worked extremely well.
One commenter stated that these studies confirm that measurement
interference cannot be eliminated by blank correction and longer sample
times, and that the proposed single sample enforcement policy would not
be representative of typical mine conditions. MSHA disagrees with this
conclusion from the verification tests. The MSHA tests demonstrated
that blank correction does eliminate a source of interference. The
residual organic carbon indicated in several of the samples collected
at crushers were attributed to short sample time and normal variation
in the range of blank values. The verification tests did not address
sample time. However, when converting the mass collected to a
concentration, the mass is divided by the sample time. Dividing by a
longer time will always reduce an interference caused by a positive
bias.
Other commenters alleged that there were problems with the MSHA
personnel performing the studies. Some asserted these personnel failed
to listen to suggestions made by representatives of mine companies who
accompanied MSHA in their facilities during in-mine testing,
suggestions which they assert would have corrected asserted problems in
the testing procedure. Others simply assert that the MSHA personnel
were biased, manipulated the data, and tried to conform the study
results to those they wanted to find. It was also asserted that any
potential for bias should have been removed through independent peer
review of the results, or performance or confirmation of the studies by
independent personnel or laboratories.
The tests were designed and conducted by personnel from MSHA's
Pittsburgh Safety and Heath Technology's Dust Division. This laboratory
at this facility is AIHA accreditated, and its personnel are among the
foremost experts in particulate sampling analysis in the mining
industry. They are widely published and are accustomed to performing
work that must survive legal and scientific scrutiny. Moreover, the
personnel designing and performing these studies have more experience
than anybody else with dust sampling in general, and with this
particular measurement application. While the agency welcomes scrutiny
of its work, and repetition by others, it also recognizes that such
efforts take time. In this case, the agency elected to conduct tests to
address specific concerns, given its obligation to respond to the risks
to miners reviewed in Part III of this preamble. It did so using a
sound study design and expert personnel, and has made the detailed
results of its studies a matter of public record.
In this regard, a number of commenters made reference to a study
currently being conducted by NIOSH of possible interferences with the
5040 method. Some of these commenters provided MSHA with a copy of what
is apparently the final protocol for the study, asserted that it would
provide better information than the verification studies conducted by
MSHA, and urged the agency to wait for completion of this study.
MSHA welcomes the NIOSH study, and will carefully consider its
results--and the results of any other studies of this matter--in
refining the compliance practices outlined in part IV of this preamble.
But given the agency's obligation to respond to the risks to miners
reviewed in Part III of this preamble, and the recommendations of NIOSH
to take action in light of that risk, it would be inappropriate to
await the results of another study.
Carbonates and Carbonaceous Minerals. As noted in the discussion of
the analytical method (NIOSH Method 5040), carbonates have been known
to cause an interference when determining the total carbon content of a
diesel particulate sample. Carbonates are generally in two forms--
carbonates such as limestone and dolomite and bicarbonate which is
associated with trona (soda ash). As further noted, the amount of
carbonate and bicarbonate collected on a sample can be significantly
reduced or eliminated through the use of a submicrometer impactor. If
the total carbon analysis of a sample indicates that a carbonate
interference exists after the use of a submicrometer impactor, any
remaining interfering effect may be removed or diminished using the
acidification process described in NIOSH Method 5040.
Carbonate interference can also be removed during the analytical
process by mathematically subtracting the organic carbon quantified by
the fourth peak in the thermogram. Because bicarbonate is evolved over
several temperature ranges, subtraction of only one peak does not
remove all of the interference from bicarbonate. As a result, the
sample needs to be acidified to remove all of the bicarbonate
interference.
Commenters correctly pointed out that other carbonaceous minerals
are not removed by the acidification process and in fact in some cases,
the acidification process may cause a positive bias to the elemental
carbon measurement. However, MSHA has verified that through the use of
the submicrometer impactor, which reduces the mineral dust collected,
combined with the subtraction of organic carbon quantified by the
fourth organic carbon peak, this source of interference can be
eliminated (PS&HTC-DD-505, PS&HTC-DD-509, PS&HTC-DD-510 and PS&HTC-DD-;00-523).
MSHA has verified the use of a submicron impactor to remove
carbonate interference through field and laboratory measurements. In
the field measurements, simultaneous respirable and submicron dust
samples were collected near crushing operations where there was no
diesel equipment operating. In the laboratory measurements, a aerosol
containing carbonate dust was introduced into a dust chamber and
simultaneous submicron, respirable and total dust samples were
collected. For both the field and laboratory measurements, the samples
were analyzed for carbon using NIOSH Method 5040. Results of analysis
of these samples showed that for respirable dust samples, acidification
of the sample removed the carbonate.
[[Page 5729]]
Carbonate was evolved in the fourth peak of the organic portion of the
analysis. The carbon evolved by the analysis was approximately 10
percent of the carbonate collected on the gravimetric sample, roughly
equating to 12 percent carbon contained in calcium carbonate tested
(limestone). Sampling with the submicron impactor removed the carbonate
and carbonaceous component from the sample. A commenter noted that in
the dust chamber tests, organic carbon was reported, even though the
carbonate was removed by sampling, acidification or software
integration. This organic carbon was attributed to oil vapors leaking
from the compressor that delivered the dust to the chamber. This oil
leak was reported to MSHA after the tests were completed.
Sample results further indicated that the total carbon mass
determined for the respirable diesel particulate samples was
approximately 95 percent of the diesel particulate mass determined
gravimetrically and the total carbon mass determined from the impactor
diesel particulate samples was approximately 82 percent of the
respirable value. Use of the impactor reduced the amounts of carbonate
collected on the sample by 90 percent.
The difference between the respirable total carbon determinations
and the gravimetric diesel particulate can be attributed to sulfates or
other noncarbonaceous minerals in the diesel particulate. The
difference between the submicron total carbon and the respirable total
carbon determinations is attributed to the removal of diesel
particulate particles that are greater than 0.9 micrometers in size.
The difference between the carbonate measured by NIOSH Analytical
Method 5040 and the gravimetric carbonate is attributed to impurities
in the material. The expected ratio of evolved carbon from the
carbonate to carbonate (C/CaCo3) would be 0.12 (12/(40 + 12 + 48)).
Graphitic Minerals. Commenters reported that several ores,
primarily associated with gold mines, contain graphitic carbon, and
that this carbon shows up as elemental carbon in an airborne dust
sample. MSHA has collected samples of this ore and has found that in
fact this is true (PS&HTC-DD-505, PS&HTC-DD-509, PS&HTC-DD-510). MSHA
has verified the use of a submicron impactor to remove graphitic carbon
interference through field measurements.
In the field measurements, simultaneous respirable and submicron
dust samples were collected near crushing operations where there was no
diesel equipment operating. For both the field and laboratory
measurements, the samples were analyzed for carbon using NIOSH Method
5040. Results of analysis of these samples showed that for respirable
dust samples, several g/m3 of elemental carbon
could be present in the sample.
However, MSHA has found this interference is very small, and can be
reduced still further through the use of the submicron impactor on the
sampler. The highest elemental carbon content of the ores was less than
5 percent. These ores also contain at least 20 percent respirable
silica, as determined from samples collected near crushers where diesel
particulate was not present. Based on a 20 percent respirable silica
content in the dust in the environment, the allowable respirable dust
exposure would be limited to 0.45 mg/m3. Based on a 5
percent elemental carbon content in the sample, this sample could
contain 23 g/m3 of elemental carbon. Typically 10
percent of mineral dust is less than one micron. By using the submicron
impactor, the interference from graphitic carbon in the ore would be
less than 3 g/m3. Samples collected by MSHA, near
crushing operations, using submicron impactors, did not contain
elemental carbon.
Accordingly, MSHA plans to sample for diesel particulate matter
using submicron impactors to reduce the potential interference from
carbonates, carbonaceous minerals and graphitic ores. As noted
previously, this requirement is being specifically added to the
regulation.
Oil Mist and Organic Vapors. Commenters indicated that diesel
particulate sample interference can occur from sampling around drilling
operations and from organic solvents.
To verify the existence and extent of any such interference, MSHA
collected samples at stoper drilling, jack leg drilling and face
drilling operations. The stoper drill and jack leg drill were
pneumatic. The face drill was electrohydraulic. Interference from drill
oil mist was observed for both the stoper drill and jack leg drill
operations (PS&HTC-DD-505, PS&HTC-DD-511). Respirable and submicron
samples were collected in the stope, the intake air to the stope and
the exhaust air from the stope. Interference from drill oil mist was
not found in submicron samples collected on the electrohydraulic face
drill (PS&HTC-DD-505). The oil mist interference for the stoper drill
was confined to the drill location due to the use of a high viscosity
lube grease. The amount of interference in the stope on a submicron
sample for the stoper drill was 4.5 g/m\3\ per hour of
drilling. The interference from the oil mist on the jack leg operation
extended throughout the mining stope area, but it did not extent into
the main ventilation heading. The amount of interference in the stope
on a submicron sample for the jack leg drill was 9 to 11 g/
m\3\ per hour of drilling. MSHA believes that similar interferences
could occur when miners are working near organic solvents.
Accordingly, this is an interference that can be addressed by not
sampling too close to the source of the interference. As discussed in
more detail in Part IV of this preamble, when MSHA collects compliance
samples on drilling operations that produce an oil mist, or where
organic solvents are used, personal samples will not be collected.
Instead, an area sample will be collected, upwind of the driller or
organic solvent source.
A commenter suggested that the lack of organic carbon reduction
from outside to inside the cab at Homestake Mine indicated additional
sources of organic carbon that have not been identified. MSHA believes
that the reduction in elemental but not organic carbon from outside to
inside the cab at Homestake Mine was attributed to size distribution.
The organic carbon is small enough to pass through a filter. The
organic carbon in the cab could not have been generated from a source
inside the cab or attributed to residual cigarette smoke as the air
exchange rate for the cab was one air change per minute. The cab
operator did not smoke.
Cigarette Smoke. Cigarette smoke is a form of organic carbon.
Commentors indicated that cigarette smoke can interfere with a diesel
particulate measurement when total carbon is used as the indicator of
dpm. Industry Commenters collected samples in a surface ``smoke room''
where the airflow and number of cigarettes were not monitored.
To verify the existence and the extent of any such interference,
MSHA took samples in an underground mine where controlled smoking took
place. Two series of cigarette tests were conducted. A test site was
chosen in the NIOSH, PRL, Experimental Mine. The site consisted of
approximately 75 feet of straight entry. The entry was approximately
18.5 feet wide and 6.2 feet high (115 square feet area). In the first
test, the airflow rate through the test area was 6,000 cfm and 4
cigarettes were smoked over a 120 minute period. In the second test,
the airflow was 3,000 cfm and 28 cigarettes were smoked over a 210
minute period. A control filter was used to adjust for organic carbon
present on the filter media. MSHA collected samples on the smokers,
twenty-five feet upwind of the smokers,
[[Page 5730]]
twenty-five feet downwind of the smokers and fifty feet downwind of the
smokers. Results of the underground test did verify that smoking could
be an interference on a dpm measurement.
Analysis of the thermogram from the smoking test showed that
cigarette smoke showed up only in the organic portion of the analysis.
In this test with the cigarette smoke, a fifth organic peak was
observed. This peak contributed approximately 0.5 g/m\2\ to
the analysis. This would be equivalent to an 8 hour full shift
concentration of 5 g/m\3\. The thermogram otherwise is not
distinguishable from the organic portion of a thermogram for a diesel
particulate sample. Analysis of the thermogram indicated that 30
percent of the organic carbon appeared in the first organic peak, 15
percent appeared in the second organic peak, 10 percent appeared in the
third organic peak, 25 percent of the cigarette smoke appeared in the
fourth organic peak, and 20 percent of the cigarette smoke appeared in
the fifth organic peak. While the amount of carbon identified by the
fourth organic peak can be quantified and mathematically subtracted
from the amount of total carbon measured, the remaining three peaks,
representing 83 percent of the total carbon associated with smoking,
would be an interferrant to the diesel particulate matter measurement.
However, the effect of cigarette smoke was even more localized to
the smoker than the oil mist was to the stoper or jack leg drill
operator. Twenty five feet upwind of the smoker, no carbon attributed
to cigarette smoke was detected. For the smoker, each cigarette smoked
would add 5 to 10 g/m\3\ to the exposure, depending on the
airflow. Smoking 10 cigarettes would add 50 to 100 g/m\3\ to a
worker's exposure. At both twenty five feet and fifty feet downwind of
the smoker, after mixing with the ventilating air, the contribution of
carbon attributed to smoking was reduced to 0.3 g/m\3\ for
each cigarette smoked. Sampling twenty-five to fifty feet down wind of
a worker smoking 10 cigarettes per day would add no more than 3
g/m\3\ to the worker's exposure (PS&HTC-DD-518). The air
velocities in this test (30 to 60 feet per minute) were relatively low
compared to typical mine air velocities. The interference would be even
less at the higher air velocities normally found in mines.
Accordingly, as discussed in more detail in Part IV of this
preamble, when MSHA collects compliance samples, miners will be
requested not to smoke. If a miner does want to smoke while being
sampled, and is not prohibited from doing so by the mine operator, the
inspector will collect an area sample a minimum of twenty-five feet
upwind or downwind of the smoker. Smokers working inside cabs will not
be sampled.
Summary of Conclusions from Verification Studies. In summary, MSHA
was able to draw the following conclusions from these studies:
As specified in NIOSH Method 5040, it is essential to use
a blank to correct organic carbon measurements.
Contamination (interference) from carbonate and
carbonaceous minerals is evolved in the fourth organic peak of the
thermogram.
Interference from graphitic minerals may appear in the
elemental carbon portion of the analysis.
Interference from cigarette smoke and oil mist from
pneumatic drills appears in several peaks of the organic analysis.
Use of the submicron impactor removes the mineral
interference from carbonate, carbonaceous minerals and graphitic
minerals.
Acidification is required to remove the interference from
bicarbonate which maybe evolved in several of the organic peaks.
Subtraction of the fourth organic peak by software
integration can be used to correct for interference from carbonaceous
minerals.
Interference from cigarette smoke and oil mist from
pneumatic drills is localized. It can be avoided by sampling upwind or
downwind of the interfering source.
Total carbon from cigarettes smoke and oil mist are small
compared to emissions from a diesel engine.
Sampling can be conducted down wind of the interfering
source after the contaminated air current has been diluted with another
air current.
The magnitude of interferences measured during the verifications
were small compared to the levels of total carbon measured in
underground mines (as reported in Part III of this preamble). The
discussion of section 5061 in Part IV of this preamble provides further
information on how MSHA will take this information about interferences
into account in compliance sampling; in addition, MSHA will provide
specific guidance to inspectors as to how to avoid interferences when
taking compliance samples.
(4) Limiting the Public's Exposure to Diesel and Other Fine
Particulates--Ambient Air Quality Standards.
Pursuant to the Clean Air Act, the Federal Environmental Protection
Agency (EPA) is responsible for setting air pollution standards to
protect the public from toxic air contaminants. These include standards
to limit exposure to particulate matter. The pressures to comply with
these limits have an impact upon the mining industry, which limits
various types of particulate matter into the environment during mining
operations, and a special impact on the coal mining industry whose
product is used extensively in particulate emission generating power
facilities. But those standards hold interest for the mining community
in other ways as well, for underlying some of them is a large body of
evidence on the harmful effects of airborne particulate matter on human
health. Increasingly, that evidence has pointed toward the risks of the
smallest particulates--including the particles generated by diesel
engines.
This section provides an overview of EPA's rulemaking efforts to
limit the ambient air concentration of particulate matter, including
its recent particular focus on diesel and other fine particulates.
Additional and up-to-date information about the most current rulemaking
in this regard is available on EPA's Web site, http://www.epa.gov/ttn/
oarpg/naaqsfin/.
EPA is also engaged in other work of interest to the mining
community. Together with some state environmental agencies, EPA has
actually established limits on the amount of particulate matter that
can be emitted by diesel engines. This topic is discussed in the next
section of this Part (section 5). Environmental regulations also
establish the maximum sulfur content permitted in diesel fuel, and such
sulfur content can be an important factor in dpm generation. This topic
is discussed in section 6 of this Part. In addition, EPA and some state
environmental agencies have also been exploring whether diesel
particulate matter is a carcinogen or a toxic material at the
concentrations in which it appears in the ambient atmosphere.
Discussion of these studies can be found in Part III of this preamble.
Background. Air quality standards involve a two-step process:
standard setting by EPA, and implementation by each State.
Under the law, EPA is specifically responsible for reviewing the
scientific literature concerning air pollutants, and establishing and
revising National Ambient Air Quality Standards (NAAQS) to minimize the
risks to health and the environment associated with such pollutants.
This review is to be conducted every five years. Feasibility of
compliance by pollution sources is not supposed to be a factor in
establishing NAAQS. Rather, EPA is required to set the level that
provides
[[Page 5731]]
``an adequate margin of safety'' in protecting the health of the
public.
Implementation of each national standard is the responsibility of
the states. Each must develop a state implementation plan that ensures
air quality in the state consistent with the ambient air quality
standard. Thus, each state has a great deal of flexibility in targeting
particular modes of emission (e.g., mobile or stationary, specific
industry or all, public sources of emissions vs. private-sector
sources), and in what requirements to impose on polluters. However, EPA
must approve the state plans pursuant to criteria it establishes, and
then take pollution measurements to determine whether all counties
within the state are meeting each ambient air quality standard. An area
not meeting an NAAQS is known as a ``nonattainment area''.
TSP. Particulate matter originates from all types of stationary,
mobile and natural sources, and can also be created from the
transformation of a variety of gaseous emissions from such sources. In
the context of a global atmosphere, all these particles are mixed
together, and both people and the environment are exposed to a
``particulate soup'' the chemical and physical properties of which vary
greatly with time, region, meteorology, and source category.
The first ambient air quality standards dealing with particulate
matter did not distinguish among these particles. Rather, the EPA
established a single NAAQS for ``total suspended particulates'', known
as ``TSP.'' Under this approach, the states could come into compliance
with the ambient air requirement by controlling any type or size of
TSP. As long as the total TSP was under the NAAQS--which was
established based on the science available in the 1970s--the state met
the requirement.
PM10. When the EPA completed a new review of the
scientific evidence in the mid-eighties, its conclusions led it to
revise the particulate NAAQS to focus more narrowly on those
particulates less than 10 microns in diameter, or PM10. The
standard issued in 1987 contained two components: an annual average
limit of 50 g/m\3\, and a 24-hour limit of 150 g/
m\3\. This new standard required the states to reevaluate their
situations and, if they had areas that exceeded the new PM10
limit, to refocus their compliance plans on reducing those particulates
smaller than 10 microns in size. Sources of PM10 include
power plants, iron and steel production, chemical and wood products
manufacturing, wind-blown and roadway fugitive dust, secondary aerosols
and many natural sources.
Some state implementation plans required surface mines to take
actions to help the state meet the PM10 standard. In
particular, some surface mines in Western states were required to
control the coarser particles--e.g., by spraying water on roadways to
limit dust. The mining industry has objected to such controls, arguing
that the coarser particles do not adversely impact health, and has
sought to have them excluded from the EPA ambient air standards.
PM2.5. The next scientific review was completed in 1996,
following suit by the American Lung Association and others. A proposed
rule was published in November of 1996, and, after public hearings and
review by the Office Management and Budget, a final rule was
promulgated on July 18, 1997. (62 FR 38651).
The new rule further modifies the standard for particulate matter.
Under the new rule, the existing national ambient air quality standard
for PM10 remains basically the same--an annual average limit
of 50 g/m3 (with some adjustment as to how this is
measured for compliance purposes), and a 24-hour ceiling of 150
g/m3. In addition, however, a new NAAQS has now
been established for ``fine particulate matter'' that is less than 2.5
microns in size. The PM2.5 annual limit is set at 15
g/m3, with a 24-hour ceiling of 65 g/
m3.
The basis for the PM2.5 NAAQS is a large body of
scientific data suggesting that particles in this size range are the
ones responsible for the most serious health effects associated with
particulate matter. The evidence was thoroughly reviewed by a number of
scientific panels through an extended process. The proposed rule
resulted in considerable press attention, and hearings by Congress, in
which this scientific evidence was further discussed. Moreover,
challenges to EPA's determination that this size category warranted
rulemaking were rejected by a three judge panel of the DC Circuit
Court. (American Trucking Association vs. EPA, 275 F.3d 1027).
Second, the majority of the panel agreed with challenges to the
EPA's determination to keep the existing requirements on PM10 as a
surrogate for the coarser particulates in this category (those
particulates between 2.5 and 10 microns in diameter); instead, the
panel ordered EPA to develop a new standard for this size category.
(Op.Cit., *23.)
Implications for the Mining Community. As noted earlier in this
part, diesel particulate matter is mostly less than 1.0 micron in size.
It is, therefore, a fine particulate; indeed, in some regions of the
country, diesel particulate generated by highway and off-road vehicles
constitutes a significant portion of the ambient fine particulate (June
16, 1997, PM-2.5 Composition and Sources, Office of Air Quality
Planning and Standards, EPA). Moreover, as noted in Part III of this
preamble, some of the scientific studies of health risk from fine
particulates used to support the EPA rulemaking were conducted in areas
where the major fine particulate was from diesel emissions.
Accordingly, MSHA has concluded that it must consider the body of
evidence of human health risk from environmental exposure to fine
particulates in assessing the risk of harm to miners of occupational
exposure to diesel particulate. Comments on the appropriateness of the
conclusion by MSHA, and whether MSHA should be working on a fine
particulate standard rater than just one focused on diesel particulate
are reviewed in Part III.
(5) The Effects of Existing Standards--MSHA Standards on Diesel Exhaust
Gases (CO, CO2, NO, NO2, and SO2), and
EPA Diesel Engine Emission Standards--on the Concentration of dpm in
Underground Metal and Nonmetal Mines
With the exception of diesel engines used in certain
classifications of gassy mines, MSHA does not require that the
emissions from diesel engines used in underground metal and nonmetal
mines, as measured at the tailpipe, meet certain minimum standards of
cleanliness. (Some states may require engines used in underground metal
and nonmetal mines to be MSHA Approved.) This is in contrast to
underground coal mines, where only engines which meet certain standards
with respect to gaseous emissions are ``approved'' for use in
underground coal mines. Indeed, as discussed in section 7 of this part,
the whole underground coal mine fleet must now consist of approved
engines, and the engines must be maintained in approved condition.
While such restrictions do not directly control dpm emissions of
underground coal equipment, they do have some indirect impact on them.
MSHA does have some requirements for underground metal and nonmetal
mines that limit the exposure of miners to certain gases emitted by
diesel engines. Accordingly, those requirements are discussed here.
Engine emissions of dpm in underground metal and nonmetal mines are
gradually being impacted by Federal environmental regulations,
supplemented in some cases by State restrictions. Over time, these
regulations have required, and are continuing to
[[Page 5732]]
require, that new diesel engines meet tighter and tighter standards on
dpm emissions. As these cleaner engines replace or supplement older
engines in underground metal and nonmetal mines, they can significantly
reduce the amount of dpm emitted by the underground fleet. Much of this
section reviews developments in this area. Although this subject was
discussed in the preamble of the proposed dpm rule (63 FR 58130 et
seq.), the review here updates the relevant information.
MSHA Limitations on Diesel Gases. MSHA limits on the exposure of
miners to certain gases in underground mines are listed in Table II-2,
for both coal mines and metal/nonmetal mines, together with information
about the recommendations in this regard of other organizations. As
indicated in the table, MSHA requires mine operators to comply with gas
specific threshold limit values (TLVs) recommended by the
American Conference of Governmental Industrial Hygienists (ACGIH) in
1972 (for coal mines) and in 1973 (for metal and nonmetal mines).
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[[Page 5734]]
To change an exposure limit at this point in time requires a
regulatory action; the rule does not provide for their automatic
updating. In 1989, MSHA proposed changing some of these gas limits in
the context of a proposed rule on air quality standards. (54 FR 35760).
Following opportunity for comment and hearings, a portion of that
proposed rule, concerning control of drill dust and abrasive blasting,
has been promulgated, but the other components are still under review.
One commenter expressed concern that MSHA would attempt to regulate
dpm together with diesel exhaust gases based on their additive or
combined effects. As discussed in greater detail in Part IV of this
preamble, MSHA does not, at this time, have sufficient information upon
which to enforcement limits for dpm and diesel exhaust gases on the
basis of their additive or combined effects, if any.
Authority for Environmental Engine Emission Standards. The Clean
Air Act authorizes the Federal Environmental Protection Agency (EPA) to
establish nationwide standards for mobile vehicles, including those
powered by diesel engines (often referred to in environmental
regulations as ``compression ignition'' or ``CI'' engines). These
standards are designed to reduce the amount of certain harmful
atmospheric pollutants emanating from mobile sources: the mass of
particulate matter, nitrogen oxides (which as previously noted, can
result in the generation of particulates in the atmosphere),
hydrocarbons and carbon monoxide.
California has its own engine emission standards. New engines
destined for use in California must meet standards under the law of
that State. The standards are issued and administered by the California
Air Resources Board (CARB). In many cases, the California standards are
the same as the national standards; as noted herein, the EPA and CARB
have worked on certain agreements with the industry toward that end. In
other situations, the California standards may be more stringent.
Regulatory responsibility for implementation of the Clean Air Act
is vested in the Office of Transportation and Air Quality (formerly the
Office of Mobile Sources), part of the Office of Air and Radiation of
the EPA. Some of the discussion which follows was derived from
materials which can be accessed from the agency's home page on the
World Wide Web at (http://www.epa.gov/omswww/omshome.htm). Information
about the California standards may be found at the CARB home page at
(http://www.arb.ca.gov/homepage.htm).
Diesel engines are generally divided into three broad categories
for purposes of engine emissions standards, in accordance with the
primary use for which the type of engine is designed: (1) light duty
vehicles and light duty trucks (i.e., those engines designed primarily
to power passenger transport or transportation of property); (2) heavy
duty highway engines (i.e., those designed primarily to power over-the-
road truck hauling); and (3) nonroad vehicles (i.e., those engines
designed primarily to power small equipment, construction equipment,
locomotives and other non-highway uses).
The exact emission standards which a new diesel engine must meet
varies with engine category and the date of manufacture. Through a
series of regulatory actions, EPA has developed a detailed
implementation schedule for each of the three engine categories noted.
The schedule generally forces technology while taking into account
certain technological realities.
Detailed information about each of the three engine categories is
provided below; a summary table of particulate matter emission limits
is included at the end of the discussion.
EPA Emission Standards for Light-Duty Vehicles and Light Duty
Trucks.\2\
---------------------------------------------------------------------------
\2\ The discussion focuses on the particulate matter
requirements for light duty trucks, although the current pm
requirement for light duty vehicles is the same. The EPA regulations
for these categories apply to the unit, rather than just to the
engine itself; for heavy-duty highway engines and nonroad engines,
the regulations attach to the engines.
---------------------------------------------------------------------------
Current light-duty vehicles generally comply with the Tier 1 and
National LEV emission standards. Particulate matter emission limits are
found in 40 CFR Part 86. In 1999, EPA issued new Tier 2 standards that
will be applicable to light-duty cars and trucks beginning in 2004.
With respect to pm, the new rules phase in tighter emissions limits to
parts of production runs for various subcategories of these engines
over several years; by 2008, all light duty trucks must limit pm
emissions to a maximum of 0.02 g/mi. (40 CFR 86.1811-04(c)). Engine
manufacturers may, of course, produce complying engines before the
various dates required.
EPA Emissions Standards for Heavy-Duty Highway Engines. In 1988, a
standard limiting particulate matter emitted from the heavy duty
highway diesel engines went into effect, limiting dpm emissions to 0.6
g/bhp-hr. The Clean Air Act Amendments of 1990 and associated
regulations provided for phasing in even tighter controls on
NOX and particulate matter through 1998. Thus, engines had
to meet ever tighter standards for NOX in model years 1990,
1991 and 1998; and tighter standards for PM in 1991 (0.25 g/bhp-hr) and
1994 (0.10 g/bhp-hr). The latter remains the standard for PM from these
engines for current production runs (40 CFR 86.094-11(a)(1)(iv)(B)).
Since any heavy duty highway engine manufactured since 1994 must meet
this standard, there is a supply of engines available today which meet
this standard. These engines are used in mining in the commercial type
pickup trucks.
New standards for this category of engines are gradually being put
into place. On October 21, 1997, EPA issued a new rule for certain
gaseous emissions from heavy duty highway engines that will take effect
for engine model years starting in 2004 (62 FR 54693). The rule
establishes a combined requirement for NOX and Non-methane
Hydrocarbon (NMHC). The combined standard is set at 2.5 g/bhp-hr, which
includes a cap of 0.5 g/bhp-hr for NMHC. EPA promulgated a rulemaking
on December 22, 2000 (65 FR 80776) to adopt the next phase of new
standards for these engines. EPA is taking an integrated approach to:
(a) Reduce the content of sulfur in diesel fuel; and thereafter, (b)
require heavy-duty highway engines to meet tighter emission standards,
including standards for PM. The purpose of the diesel fuel component of
the rulemaking is to make it technologically feasible for engine
manufacturers and emissions control device makers to produce engines in
which dpm emissions are limited to desired levels in this and other
engine categories. The EPA's rule will reduce pm emissions from new
heavy-duty engines to 0.01 g/bhp-hr, a reduction from the current 0.1
g/bhp-hr. MSHA assumes it will be some time before there is a
significant supply of engines that can meet this standard, and the fuel
supply to make that possible.
EPA Emissions Standards for Nonroad Engines. Nonroad engines are
those designed primarily to power small portable equipment such as
compressors and generators, large construction equipment such as haul
trucks, loaders and graders, locomotives and other miscellaneous
equipment with non-highway uses. Engines of this type are the ones used
most frequently in the underground coal mines to power equipment.
Nonroad diesel engines were not subjected to emission controls as
early as other diesel engines. The 1990 Clean Air Act Amendments
specifically directed EPA to study the contribution of nonroad engines
to air pollution, and
[[Page 5735]]
regulate them if warranted (Section 213 of the Clean Air Act). In 1991,
EPA released a study that documented higher than expected emission
levels across a broad spectrum of nonroad engines and equipment (EPA
Fact Sheet, EPA420-F-96-009, 1996). In response, EPA initiated several
regulatory programs. One of these set Tier 1 emission standards for
larger land-based nonroad engines (other than for rail use). Limits
were established for engine emissions of hydrocarbons, carbon monoxide,
NOX, and dpm. The limits were phased in with model years
from 1996 to 2000. With respect to particulate matter, the rules
required that starting in model year 1996, nonroad engines from 175 to
750 hp meet a limit on pm emissions of 0.4 g/bhp-hr, and that starting
in model year 2000, nonroad engines over 750 hp meet the same limit.
Particulate matter standards for locomotive engines were set
subsequently (63 FR 18978, April, 1998). The standards are different
for line-haul duty-cycle engine and switch duty-cycle engines. For
model years from 2000-2004, the standards limit pm emissions to 0.45 g/
bhp-hr and 0.54 g/bhp-hr respectively for those engines; after model
year 2005, the limits drop to 0.20 g/bhp-hr and 0.24 g/bhp-hr
respectively.
In October 1998, EPA established additional standards for nonroad
engines (63 FR 56968). Among these are gaseous and particulate matter
limits for the first time (Tier 1 limits) for nonroad engines under 50
hp. Tier 2 emissions standards for engines between 50 and 175 hp
include pm standards for the first time. Moreover, they establish Tier
2 particulate matter limits for all other land-based nonroad engines
(other than locomotives which already had Tier 2 standards). Some of
the non-particulate emissions limits set by the 1998 rule are subject
to a technology review in 2001 to ensure that the levels required to be
met are feasible; EPA has indicated that in the context of that review,
it intends to consider further limits for particulate matter, including
transient emission measurement procedures. Because of the phase-in of
these Tier 2 pm standards, and the fact that some manufacturers will
produce engines meeting the standard before the requirements go into
effect, there are or soon will be some Tier 2 pm engines in some sizes
available, but it is likely to be a few years before a full size range
of Tier 2 pm nonroad engines is available.
Table II-3, EPA NonRoad Engine PM Requirements, provides a full
list of the EPA required particulate matter limitations on nonroad
diesel engines. For example, a nonroad engine of 175 hp produced in
2001 must meet a standard of 0.4 g/hp-hr; a similar engine produced in
2003 or thereafter must meet a standard of 0.15 g/hp-hr.
Table II-3.--EPA Nonroad Engine PM Requirements
------------------------------------------------------------------------
Year first PM limit (g/
kW range Tier applicable kW-hr)
------------------------------------------------------------------------
kW8.............................. 1 2000 1.00
2 2005 0.80
8kW19................. 1 2000 0.80
19kW37................ 1 1999 0.80
2 2004 0.60
37kW75................ 1 1998 ...........
2 2004 0.40
75kW130............... 1 1997 ...........
2 2003 0.30
130kW225.............. 1 1996 0.54
2 2003 0.20
225kW450.............. 1 1996 0.54
2 2001 0.20
450kW560.............. 1 1996 0.54
2 2002 0.20
kW>560........................... 1 2000 0.54
2 2006 0.20
------------------------------------------------------------------------
The Impact of EPA Engine Emission Standards on the Underground
Metal and Nonmetal Mining Fleet. In the mining industry, engines and
equipment are often purchased in used condition. Thus, many of the
diesel engines in an underground mine's fleet may only meet older
environmental emission standards, or no environmental standards at all.
By requiring that underground coal mine engines be approved, MSHA
regulations have led to a less polluting fleet in that sector than
would otherwise be the case. Many highly polluting engines have been
barred or phased out as a result. As noted in Part IV of this preamble,
such a requirement for the underground metal and nonmetal sector is
being added by this rulemaking; however, it will be some time before
its effects are felt. Moreover, although the environmental tailpipe
requirements will bring about gradual reduction in the overall
contribution of diesel pollution to the atmosphere, the beneficial
effects on mining atmospheres may require a long timeframe absent
actions that accelerate the turnover of mining fleets to engines that
emit less dpm.
The Question of Nanoparticles. Comments received from several
commenters on the proposed rule for diesel particulate matter exposure
of underground coal miners raised questions relative to
``nanoparticles'; i.e., particles found in the exhaust of diesel
engines that are characterized by diameters less than 50 nanometers
(nm). As the topic may be of interest to this sector as well, MSHA's
discussion on the topic is being repeated in this preamble for
informational purposes.
One commenter was concerned about recent indications that
nanoparticles may pose more of a health risk than the larger particles
that are emitted from a diesel engine. This commenter submitted
information demonstrating that nanoparticles emitted from the engine
could be effectively removed from the exhaust using aftertreatment
devices such as ceramic traps. Another commenter was concerned that
MSHA's proposed rule for underground coal mines is based on removing
95% of the particulate by mass. His concern was focused on the fact
that this reduction in mass was attributed to those particles
[[Page 5736]]
greater than 0.1m but less than 1m and did not
address the recent scientific hypothesis that it may be the very small
nanopaticles that are responsible for adverse health effects. Based on
the recent specific information on the potential health effects
resulting from exposure to nanoparticles, this commenter did not
believe that the risk to cancer would be reduced if exposure levels to
nanoparticles increased. He indicated that studies suggest that the
increase in nanoparticles will exceed 6 times their current levels.
Current environmental emission standards established by EPA and
CARB, and the particulate index calculated by MSHA, focus on the total
mass of diesel particulate matter emitted by an engine--for example,
the number of grams per some unit of measure (i.e., grams/brake-
horsepower). Thus, the technology being developed by the engine
industry to meet the standards accordingly focuses on reducing the mass
of dpm being emitted from the engine.
There is some evidence, however, that some aspects of this new
technology, particularly fuel injection, is resulting in an increase in
the number of nanoparticles being emitted from the engine.
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[[Page 5738]]
The formation of particulates starts with particle nucleation
followed by subsequent agglomeration of the nuclei particles into an
accumulation mode. Thus, as illustrated in Figure II-3, the majority of
the mass of dpm is found in the accumulation mode, where the particles
are generally between 0.1 and 1 micron in diameter. However, when
considering the number of particles emitted from the engine, more than
half and sometimes almost all of the particles (by number) are in the
nuclei mode.
Various studies have demonstrated that the size of the particles
emitted from the new low emission diesel engines, has shifted toward
the generation of nuclei mode particles. One study compared a
comparable 1991 engine to its 1988 counterpart. The total PM mass in
the newer engine was reduced by about 80%; but the new engine generated
thousands of times more particles than the older engine (3000 times as
much at 75 percent load and about 14,000 times as much at 25 percent
load). One hypothesis offered for this phenomenon is that the cleaner
engines produce less soot particles on which particulates can condense
and accumulate, and hence they remain in nuclei mode. The accumulation
particles act as a ``sponge'' for the condensation and/or adsorption of
volatile materials. In the absence of that sponge, gas species which
are to become liquid or solid will nucleate to form large numbers of
small particles (diesel.net technology guide). Mayer, while pointing
out that nanoparticle production was a problem with older engines as
well, concurs that the technology being used to clean up pollution in
newer engines is not having any positive impact on nanoparticle
production. While there is scientific evidence that the newer engines,
designed to reduce the mass of pollutants emitted from the diesel
engine, emit more particles in the nuclei mode, quantifying the
magnitude of these particles has been difficult because as dpm is
released into the atmosphere the diesel particulate undergoes very
complex changes. In addition, current testing procedures can produce
spurious increases in the number of nanoparticles that would not
necessarily occur under more realistic atmospheric conditions.
Experimental work conducted at WVU (Bukarski) indicate that
nanoparticles are not generated during the combustion process, but
rather during various physical and chemical processes which the exhaust
undergoes in after treatment systems.
While current medical research findings indicate that small
particulates, particularly those below 2m in size, may be more
harmful to humans than the larger ones, much more medical research and
diesel emission studies are needed to fully characterize diesel
nanoparticles emissions and their impact on human health. If
nanoparticles are found to have an adverse health impact by virtue of
size and number, it could require significant adjustments in
environmental engine emission regulation and technology. It could also
have implications for the type of controls utilized, with some
asserting that aftertreatment filters are the only effective way to
limit the emission of nanoparticles and others asserting that
aftertreatment filters may under certain circumstances limit the number
of nanoparticles.
Research on nanoparticles and their health effects is currently a
topic of investigation. (Bagley et al., 1996, EPA Grant). Based on the
comments received and a review of the literature currently available on
the nanoparticle issue, MSHA believes that, at this time, promulgation
of the final rules for underground coal and metal and nonmetal mines is
necessary to protect miners. The nanoparticle issues discussed above
will not be resolved for some time because of the extensive research
required to address the questions raised.
(6) Methods for controlling dpm concentrations in underground metal and
nonmetal mines
As discussed in the last section, the introduction of new engines
underground will certainly play a significant role in reducing the
concentration of dpm in underground metal/nonmetal mines. There are,
however, many other approaches to reducing dpm concentrations and
occupational exposures to dpm in underground metal/nonmetal mines.
Among these are: aftertreatment devices to eliminate particulates
emitted by an engine; altering fuel composition to minimize engine
particulate emission; maintenance practices and diagnostic systems to
ensure that fuel, engine and aftertreatment technologies work as
intended to minimize emissions; enhancing ventilation to reduce
particulate concentrations in a work area; enclosing workers in cabs or
other filtered areas to protect them from exposure; and work and fleet
practices that reduce miner exposures to emissions.
As noted in section 9 of this Part, information about these
approaches was solicited from the mining community in a series of
workshops in 1995, and highlights were published by MSHA as an appendix
to the proposed rule on dpm ``Practical Ways to Control Exposure to
Diesel Exhaust in Mining--a Toolbox.'' During the hearings and in
written comments on this rulemaking, mention was made of all these
control methods.
This section provides updated information on two methods for
controlling dpm emissions: aftertreatment devices and diesel fuel
content. There was considerable comment on aftertreatment devices
because MSHA's proposed rule would require high-efficiency particulate
filters be installed on a certain percentage of the fleet in order to
meet both the interim and final dpm concentration; and the current and
potential efficiency of such devices remains an important issue in
determining the technological and economic feasibility of the final
rule. Moreover, some commenters strongly favored the use of oxidation
catalytic converters, a type of aftertreatment device used to reduce
gaseous emission but which can also impact dpm levels. Accordingly,
information about such devices is reviewed here. With respect to diesel
fuel composition, a recent rulemaking initiative by EPA, and actions
taken by other countries in this regard, are discussed here because of
the implications of such developments for the mining community.
Emissions aftertreatment devices. One of the most discussed
approaches to controlling dpm emissions involves the use of devices
placed on the end of the tailpipe to physically trap diesel particulate
emissions and thus limit their discharge into the mine atmosphere.
These aftertreatment devices are often referred to as ``particle
traps'' or ``soot traps'', but the term filter is often used. The two
primary categories of particulate traps are those composed of ceramic
materials (and thus capable of handling uncooled exhaust), and those
composed of paper materials (which require the exhaust to first be
cooled). Typically, the latter are designed for conventional
permissible equipment mainly used in coal mining which have water
scrubbers installed which cool the exhaust. However, another
alternative that is now utilized in coal is the ``dry system
technology'' which cools the diesel exhaust with a heat exchanger and
then uses a paper filter. The dry system was first developed for oil
shale mining applications where permissibility was required. However,
when development of the oil shale industry faltered, manufacturers
looked to coal mining for
[[Page 5739]]
application of the dry system technology. However, dry systems could be
used as an alternative to the wet scrubbers for the relatively small
number of permissible machines used in the metal/nonmetal industry. In
addition, ``oxidation catalytic converters,'' devices used to limit the
emission of diesel gases, and ``water scrubbers'', devices used to cool
the exhaust gases, are discussed here as well, because they also can
have a significant effect on limiting particle emission.
Water Scrubbers. Water scrubbers are devices added to the exhaust
system of certain diesel equipment. Water scrubbers are essentially
metal boxes containing water through which the diesel exhaust gas is
passed. The exhaust gas is cooled, generally to below 170 degrees F. A
small fraction of the unburned hydrocarbons are condensed and remain in
the water along with a portion of the dpm. Tests conducted by the
former Bureau of Mines and others indicate that no more than 20 to 30
percent of the dpm is removed. This information was presented in the
Toolbox publication. The water scrubber does not remove any of the
carbon monoxide, the oxides of nitrogen, or any other gaseous emission
that remains a gas at room temperature so their effectiveness as
aftertreatment devices is questionable.
The water scrubber does serve as an effective spark and flame
arrester and as a means to cool the exhaust gas when permissibility is
required. Consequently, it is used in the majority of the permissible
diesel equipment in mining as part of the safety components needed to
gain MSHA approval.
The water scrubber has several operating characteristics which keep
it from being a candidate for use as an aftertreatment device on
nonpermissible equipment. The space required on the vehicle to store
sufficient water for an 8 hour shift is not available on some
equipment. Furthermore, the exhaust contains a great deal of water
vapor which condenses under some mining conditions creating a fog which
can adversely effect visibility. Also, operation of the equipment on
slopes can cause the water level in the scrubber to change resulting in
water being blown out the exhaust pipe. Control devices are sometimes
placed within the scrubber to maintain the appropriate water level.
Because these devices are in contact with the water through which the
exhaust gas has passed, they need frequent maintenance to insure that
they are operating properly and have not been corroded by the acidic
water created by the exhaust gas. The water scrubber must be flushed
frequently to remove the acidic water and the dpm and other exhaust
residue which forms a sludge that adversely effects the operation of
the unit. These problems, coupled with the relatively low dpm removal
efficiency, have prevented widespread use of water scrubbers as a dpm
control device on nonpermissible equipment.
Oxidation Catalytic Converters. Oxidation catalytic converters
(OCCs) were among the first devices added to diesel engines in mines to
reduce the concentration of harmful gaseous emissions discharged into
the mine environment. OCCs began to be used in underground mines in the
1960's to control carbon monoxide, hydrocarbons and odor. That use has
been widespread. It has been estimated that more than 10,000 OCCs have
been put into the mining industry over the years.
Several of the harmful emissions in diesel exhaust are produced as
a result of incomplete combustion of the diesel fuel in the combustion
chamber of the engine. These include carbon monoxide and unburned
hydrocarbons including harmful aldehydes. Catalytic converters, when
operating properly, remove significant percentages of the carbon
monoxide and unburned hydrocarbons. Higher operating temperatures,
achieved by hotter exhaust gas, improve the conversion efficiency.
Oxidation catalytic converters operate by, in effect, continuing
the combustion process outside the combustion chamber. This is
accomplished by utilizing the oxygen in the exhaust gas to oxidize the
contaminants. A very small amount of material with catalytic
properties, usually platinum or some combination of the noble metals,
is deposited on the surfaces of the catalytic converter over which the
exhaust gas passes. This catalyst allows the chemical oxidation
reaction to occur at a lower temperature than would normally be
required.
For the catalytic converter to work effectively, the exhaust gas
temperature must be above 370 degrees Fahrenheit for carbon monoxide
and 500 degrees Fahrenheit for hydrocarbons. Most converters are
installed as close to the exhaust manifold as possible to minimize the
heat loss from the exhaust gas through the walls of the exhaust pipe.
Insulating the segment of the exhaust pipe between the exhaust manifold
and the catalytic converter extends the portion of the vehicle duty
cycle in which the converter works effectively.
The earliest catalytic converters for mining use consisted of
alumina pellets coated with the catalytic material and enclosed in a
container. The exhaust gas flowed through the pellet bed and the
exhaust gas came into contact with the catalyst. Designs have evolved,
and the most common design is a metallic substrate, formed to resemble
a honeycomb, housed in a metal shell. The catalyst is deposited on the
surfaces of the honeycomb. The exhaust gas flows through the honeycomb
and comes into contact with the catalyst.
Soon after catalytic converters were introduced, it became apparent
that there was a problem brought about by the sulfur found in diesel
fuels in use at that time. Most diesel fuels in the United States
contained anywhere from 0.25 to 0.50 percent sulfur or more on a mass
basis. In the combustion chamber, this sulfur was converted to
SO2, SO3, or SO4 in various
concentrations, depending on the engine operating conditions. In
general, most of the sulfur was converted to gaseous SO2.
When exhaust containing the gaseous sulfur dioxide passed through the
catalytic converter, a large proportion of the SO2 was
converted to solid sulphates which are in fact, diesel particulate.
Sulfates can ``poison'' the catalyst, severely reducing its life.
Recently, as described elsewhere in this preamble, the EPA required
that diesel fuel used for over the road trucks contain no more than 500
ppm sulfur. This action made low sulfur fuel available throughout the
United States. MSHA, in its recently promulgated regulations for the
use of diesel powered equipment in underground coal mines requires that
this low sulfur fuel be used. MSHA is now extending this requirement
for low sulfur fuel (500ppm) to underground metal/nonmetal mines in
this final rule. When the low sulfur fuel is burned in an engine and
passed through a converter with a moderately active catalyst, only
small amounts of SO2 and additional sulfate based
particulate are created. However, when a very active catalyst is used,
to lower the operating temperature of the converter or to enhance the
CO removal efficiency, even the low sulfur fuel has sufficient sulfur
present to create an SO2 and sulfate based particulate
problem. Consequently, as discussed later in this section, the EPA has
notified the public of its intentions to promulgate regulations that
would limit the sulfur content of future diesel fuel to 15 ppm for on-
highway use in 2006.
The particulate reduction capabilities of some OCCs are significant
in gravimetric terms. In 1995, the EPA implemented standards requiring
older buses in urban areas to reduce the dpm emissions from rebuilt bus
engines. (40
[[Page 5740]]
CFR 85.1403). Aftertreatment manufacturers developed catalytic
converter systems capable of reducing dpm by 25%. Such systems are
available for larger diesel engines common in the underground metal and
nonmetal sector. However, as has been pointed out by Mayer, the portion
of particulate mass that seems to be impacted by OCCs is the soluble
component, and this is a smaller percentage of particulate mass in
utility vehicle engines than in automotive engines. Moreover, some
measurements indicate that more than 40% of NO is converted to more
toxic NO2, and that particulate mass actually increases
using an OCC at full load due to the formation of sulfates. In
summation, Mayer concluded that the OCCs do not reduce the combustion
particulates, produce sulfate particulates, have unfavorable gaseous
phase reactions increasing toxicity, and that the positive effects are
irrelevant for construction site diesel engines. Indeed, he indicates
the negative effects outweigh the benefits. (Mayer, 1998. The Phase 1
interim data report of the Diesel Emission Control-Sulfur Effects
(DECSE) Program (a joint government-industry program to explore lower
sulfur content that is discussed in more detail later in this section)
similarly indicates that using OCCs under certain operating conditions
can increase dpm emissions due to an increase in the sulfate fraction
(DECSE Program Summary, Dec. 1999). Another commenter also notes that
oxidation catalytic activity can increase sulfates and submicron
particles under certain operating conditions.
Other commenters during the rulemaking strongly supported the use
of OCCs as an interim measure to reduce particulate and other diesel
emission to address transitory employee effects that were mentioned in
the proposed preamble. MSHA views the use of OCCs as one tool that mine
operators can use to reduce the dpm emissions from certain vehicles
alone or in combination of other aftertreatment controls to meet the
interim and final dpm standards. The overall reduction in dpm emissions
achieved with the exclusive use of an OCC is low compared to the
reductions required to meet the standards. MSHA is aware of the
negative effects produced by OCCs. However, with the use of low sulfur
fuel and a catalyst that is formulated for low sulfate production, this
problem can be resolved. Mine operators must work with aftertreatment
manufacturers to come up with the best plan for their fleet for dpm
control.
Hot gas filters. Throughout this preamble, MSHA is referring to the
particulate traps (filters) that can be used in the undiluted hot
exhaust stream from the diesel engine as hot gas filters. Hot gas
filters refer to the current commercially available particulate
filters, such as ceramic cell, woven fiber filters, sintered metal
filters, etc.
Following publication of EPA rules in 1985 limiting diesel
particulate emissions from heavy duty diesel engines, aftertreatment
devices capable of significant reductions in particulate levels began
to be developed for commercial applications.
The wall flow type ceramic honeycomb diesel particulate filter
system was initially the most promising approach. These consisted of a
ceramic substrate encased in a shock and vibration absorbing material
and covered with a protective metal shell. The ceramic substrate is
arranged in the shape of a honeycomb with the openings parallel to the
centerline. The ends of the openings of the honeycomb cells are plugged
alternately. When the exhaust gas flows through the particulate trap,
it is forced by the plugged end to flow through the ceramic wall to the
adjacent passage and then out into the mine atmosphere. The ceramic
material is engineered with pores in the ceramic material sufficiently
large to allow the gas to pass through without adding excessive back
pressure on the engine, but small enough to trap the particulate on the
wall of the ceramic material. Consequently, these units are called wall
flow traps.
Work with ceramic filters in the last few years has led to the
development of the ceramic fiber wound filter cartridge (SAE, SP-1073,
1995). The ceramic fiber has been reported by the manufacturer to have
dpm reduction efficiencies up to 80 percent. This system has been used
on vehicles to comply with German requirements that all diesel engines
used in confined areas be filtered. Other manufacturers have made the
wall flow type ceramic honeycomb dpm filter system commercially
available to meet the German standard.
The development of these devices has proceeded in response to
international and national efforts to regulate dpm emissions. However,
due to the extensive work performed by the engine manufacturers on new
technological designs of the diesel engine's combustion system, and the
use of low sulfur fuel, particulate traps turned out to be unnecessary
to comply with the EPA standards of the time for vehicle engines.
These devices proved to be very effective at removing particulate
achieving particulate removal efficiencies of greater than 90 percent.
It was quickly recognized that this technology, while not
immediately required for most vehicles, might be particularly useful in
mining applications. The former Bureau of Mines investigated the use of
catalyzed diesel particulate filters in underground mines in the United
States (BOM, RI-9478, 1993). The investigation demonstrated that
filters could work, but that there were problems associated with their
use on individual unit installations, and the Bureau made
recommendations for installation of ceramic filters on mining vehicles.
Canadian mines also began to experiment with ceramic traps in the
1980's with similar results (BOM, IC 9324, 1992). Work in Canada today
continues under the auspices of the Diesel Emission Evaluation Program
(DEEP), established by the Canadian Centre for Mineral and Energy
Technology in 1996 (DEEP Plenary Proceedings, November 1996). The goals
of DEEP are to: (1) Evaluate aerosol sampling and analytical methods
for dpm; and (2) evaluate the in-mine performance and costs of various
diesel exhaust control strategies.
Perhaps because experience is still limited, the general perception
within the mining industry of the state of this technology in recent
years is that it remains limited in certain respects; as expressed by
one commenter at one of the MSHA workshops in 1995, ``while ceramic
filters give good results early in their life cycle, they have a
relatively short life, are very expensive and unreliable.''
One commenter reported unsuccessful experiments with ceramic
filters in 1991 due to their inability to regenerate at low
temperatures, lack of reliability, high cost of purchase and
installation, and short life.
In response to the proposed rule, MSHA received a variety of
information and claims about the current efficiency of such
technologies. Commenters stated that in terms of technical feasibility
to meet the standards, the appropriate aftertreament controls are not
readily available on the market for the types and sizes of equipment
used in underground mines. Another commenter stated that MSHA has not
identified a technology capable of meeting the proposed standards at
their mine and they were not aware of any technology currently
available or on the horizon that would be capable of attaining the
standards. Yet another commenter stated that both ceramic and paper
filters are not technically feasible at their mine because of the high
operating temperatures needed to regenerate filters or the difficulties
[[Page 5741]]
presented by periodic removal of the filters for regeneration. Periodic
removal of fragile ceramic filters subjects them to chipping and
cracking and requires a large inventory of surplus filters. Commenter
also stated that paper filters require exhaust gas cooling so that the
paper filter does not burn. Commenter stated that they have been
working with a manufacturer on installing one of these on a piece of
equipment, but it is experimental and this installation was the first
time a paper filter would be used on equipment of this size and type.
In response to the paper filter comment, dry system technology as
described above was first tested on a large haul truck used in oil
shale mining and then later applied to coal mining equipment. Paper
filter systems have also been successfully installed on coal mining
equipment that is identical to LHD machines used in metal/nonmetal
mines. Therefore this technology has been applied to engine of the type
and size used in metal/nonmetal mines. Commenters have stated that
filters are not feasible at this time from the above comments. However,
MSHA believes that the technology needed to reduce dpm emissions to
both the interim and final standards is feasible. Much work has
occurred in the development of aftertreatment controls, especially OCCs
and hot gas filters. Aftertreatment control manufacturers have been
improving both OCCs and ceramic type filters to provide better
performance and reliability. New materials are currently available
commercially and new filter systems are being developed especially in
light of the recent requirements in Europe and the new proposals from
the EPA. Consequently, MSHA does not agree with the commenter
concerning chipping of the traps when removed. As stated, manufacturers
have designed systems to either be removed easily or even regenerated
on the vehicle by simply plugging the unit in without removing the
filter.
Two groups in particular have been doing some research comparing
the efficiency of recent ceramic models: West Virginia University, as
part of that State's efforts to develop rules on the use of diesel-
powered equipment underground; and VERT (Verminderung der Emissionen
von Realmaschinen in Tunnelbau), a consortium of several European
agencies conducting such research in connection with major planned
tunneling projects in Austria, Switzerland and Germany to protect
occupational health and subsequent legislation in each of the three
countries restricting diesel emissions in tunneling.
The State of West Virginia legislature enacted the West Virginia
Diesel Act, thereby creating the West Virginia Diesel Commission and
setting forth an administrative vehicle to allow and regulate the use
of diesel equipment in underground coal mines in West Virginia. West
Virginia University was appropriated funds to test diesel exhaust
controls, as well as an array of diesel particulate filters. The
University was asked to provide technical support and data necessary
for the Commission to make decisions on standards for emission
controls. Even though the studies were intended for the Commission's
work for underground coal, the control technologies tested are relevant
to metal/nonmetal mines.
The University reported data on four different engines and an
assortment of configurations of available control devices, both hot gas
filters and the DST system, a system which first cools the
exhaust and then runs it through a paper filter. The range of
collection efficiencies reported for the ceramic filters and oxidation
catalysts combined fell between 65% and 78%. The highest collection
efficiency obtained using the ISO 8 mode test cycle (test cycle
described in rule) was 81% on the DST system (intended for
coal use). The University did report problems with this system that
would account for the lower than expected efficiency for a paper filter
type system.
VERT's studies of particulate traps are detailed in two articles
published in 1999 which have been widely disseminated to the diesel
community here through www.DieselNet.com. The March article focuses on
the efficiency of the traps; the April article compares the efficiency
of other approaches (OCCs, fuel reformulation, engine modifications to
reduce ultra-fine particulates) with that of the traps. Here we focus
only on the information about particulate traps.
The authors of the March article report that 29 particulate trap
systems were tested using various ceramic, metal and fiber filter media
and several regeneration systems. The authors of the March article
summarize their conclusions as follows:
The results of the 4-year investigations of construction site
engines on test rigs and in the field are clear: particulate trap
technology is the only acceptable choice among all available
measures. Traps proved to be an extremely efficient method to
curtail the finest particles. Several systems demonstrated a
filtration rate of more than 99% for ultra-fine particulates.
Specific development may further improve the filtration rate.
A two-year field test, with subsequent trap inspection,
confirmed the results pertaining to filtration characteristics of
ultra-fine particles. No curtailment of the ultra-fine particles is
obtained with any of the following: reformulated fuel, new
lubricants, oxidation catalytic converters, and optimization of the
engine combustion.
Particulate traps represent the best available technology (BAT).
Traps must therefore be employed to curtail the particulate
emissions that the law demands are minimized. This technology was
implemented in occupational health programs in Germany, Switzerland
and Austria.
On the bench tests, it appears that the traps reduce the overall
particulate matter by between 70 and 80%, with better results for solid
ultrafine particulates; under hot gas conditions, it appears the non-
solid components of particulate matter cannot be dependably retained by
these traps. Consistent with this finding, it was found that polycyclic
aromatic hydrocarbons (PAHs) decreased proportionately to the
gravimetric decrease of carbon mass. The tests also explored the impact
of additives on trap efficiency, and the impact of back pressure.
The field tests confirmed that the traps were easy to mount and
retained their reliability over time, although regeneration was
required when low exhaust temperatures failed to do this automatically.
Electronic monitoring of back pressure was recommended. In general, the
tests confirmed that a whole series of trap systems have a high
filtration rate and stable long time properties and are capable of
performing under difficult construction site conditions. Again, the
field tests indicated a very high reduction (97-99%) of particulates by
count, but a lower rate of reduction in terms of mass.
Subsequently, VERT has evaluated additional commercially available
filter systems. The filtration efficiency, expressed on a gravimetric
basis is shown in the column headed ``PMAG--without additive''. The
filtration efficiencies determined by VERT for these 6 filter systems
range from 80.7% to 94.5%. The average efficiency of these filters is
87%. MSHA will be updating the list of VERT's evaluated systems as they
become available.
VERT has also published information on the extent of dpm filter
usage in Europe as evidence that the filter technology has attained
wide spread acceptance. This information is included in the record of
the coal dpm rulemaking where it has particular significance; it is
noted here for informational purposes. The information isn't critical
in this case because operators have a choice of controls. MSHA didn't
explicitly add the latest VERT data to the Metal/
[[Page 5742]]
Nonmetal record during the latest reopening of the record. MSHA
believes this information is relevant to metal/nonmetal mining because
the tunneling equipment on which these filters are installed is similar
to metal/nonmetal equipment. VERT stated that over 4,500 filter systems
have been deployed in England, Scandinavia, and Germany. Deutz
Corporation has deployed 400 systems (Deutz's design) with full flow
burners for regeneration of filters installed on engines between 50-
600kw. The company Oberland-Mangold has approximately 1,000 systems in
the field which have accumulated an average of 8,400 operating hours in
forklift trucks, 10,600 operating hours in construction site engines,
and 19,200 operating hours in stationary equipment. The company Unikat
has introduced in Switzerland over 250 traps since 1989 and 3,000
worldwide with some operating more than 20,000 hours. German industry
annually installs approximately 1,500 traps in forklifts.
BILLING CODE 4510-43-P
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